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End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: Journal of Cosmology and Astroparticle Physics Measurement of the cosmic ray spectrum above 4 × 1018 eV using inclined events detected with the ▇▇▇▇▇_▇ ▇▇▇▇▇ Observatory To cite this article: The ▇▇▇▇▇▇ ▇▇▇▇▇ collaboration JCAP08(2015)049 View the article online for updates and enhancements. You may also like - Fundamental Physics with the Hubble Frontier Fields: Constraining Dark Matter Models with the Abundance of Extremely Faint and Distant Galaxies ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. - Persistence and nonpersistence as complementary models of identical quantum particles ▇▇▇▇▇▇ ▇▇▇▇▇ - Astrophysical Distance Scale: The AGB J- band Method. I. Calibration and a First Application ▇▇▇▇▇ ▇. ▇▇▇▇▇▇ and ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇ ournal of Cosmology and Astroparticle Physics JCAP08(2015)049 Measurement of the cosmic ray spectrum above 4 × 1018 eV using inclined events detected with the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory E-mail: auger ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showersReceived March 27, originating from ultra-high energy cosmic rays2015 Revised July 17, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations2015 Accepted July 27, based on different hadronic-interaction models2015 Published August 26, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌2015 −1.2 +1.0

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published Journal of Cosmology and Astroparticle Physics Interpretation of the depths of maximum of extensive air showers measured by IOP Publishing for Sissa Medialab 2020 JINST E-mail: the ▇▇▇▇▇_▇ ▇▇▇▇▇ Observatory To cite this article: JCAP02(2013)026 View the article online for updates and enhancements. You may also like - A RESOLVED CENSUS OF MILLIMETER EMISSION FROM TAURUS MULTIPLE STAR SYSTEMS ▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇, ▇▇▇▇ ▇. ▇▇▇▇▇▇▇, ▇▇▇▇▇ ▇. ▇▇▇▇▇▇ et al. - Handling of beam spectra in training and application of proton RBE models ▇▇▇▇ ▇▇▇▇▇▇▇▇, ▇▇▇▇ ▇▇▇▇▇▇▇ and ▇▇▇▇▇▇ ▇▇▇▇▇▇▇ - The role of the hadron initiated single electromagnetic subcascades in IACT observations ▇▇▇▇▇▇ Sobczyska ournal of Cosmology and Astroparticle Physics JCAP02(2013)026 E-mail: auger ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Received December 14, 2012 Accepted January 26, 2013 Published February 19, 2013 Abstract: Extensive . To interpret the mean depth of cosmic ray air showersshower maximum and its disper- sion, originating from ultra-high energy cosmic rays, have been suc- cessfully measured we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through the use simulations of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the groundtest mass distributions. The accurate knowledge application of the WCD response parameterization to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory data allows one to atmospheric muons performed study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources. ⃝c 2013 IOP Publishing Ltd and Sissa Medialab srl doi:10.1088/1475-7516/2013/02/026 2 A method to interpret (Xmax⟩ and σ(Xmax) 2 JCAP02(2013)026 1 Introduction‌ The most commonly used shower observables for the study of the composition of Ultra High Energy Cosmic Rays (UHECR) are the mean value of the depth of shower maximum, ⟨Xmax⟩, and its dispersion, σ(Xmax). Inferring the mass composition from these measurements is subject to some level of uncertainty. This is because their conversion to mass relies on the use of shower simulation codes which include the assumption of a hadronic interaction model. The various interaction models [1] have in common the ability to fit lower energy accelerator data. However, different physical assumptions are used to extrapolate these low energy interaction properties to higher energies. Consequently they provide different expectations for ⟨Xmax⟩ and σ(Xmax). The first aim of this paper is to discuss how the mean value of the depth of shower maximum and its dispersion can be used to interpret mass composition even in the presence of uncertainties in the hadronic interaction modeling. Furthermore, we discuss the different roles of the two observables, ⟨Xmax⟩ and σ(Xmax), with respect to mass composition. In the interpretation of data they are often used as different, and independent, aspects of the same phenomenon. However it is not true to say that both parameters reflect the cosmic ray composition to the same extent. According to the superposition model [2] ⟨Xmax⟩ is linear in ⟨ln A⟩ and therefore it actually measures mass composition for both pure and mixed compositions. But, we will show that the behaviour of σ(Xmax) is more complex to interpret as there is no one-to-one correspondence between its value and a hodoscope made given mean log mass. Only in the case of resistive plate ▇pure composition is this correspondence unique. In this paper we refine the analysis method originally proposed by ▇▇▇▇▇▇▇ (RPCs)[3, enabling us 4] and apply it to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦the Auger data. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in Collaboration has published results on the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage mean and dispersion of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions Xmax distribution at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 1018 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage In this work we apply the proposed method to convert those observables to the first moments of the RPC hodoscope to repeat with higher precision such a measurement log lnA mass distribution, namely ⟨ln A⟩ and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muonsσ2 . The presentation of the measurements, of the data analysis, and of the results paper is organised organized as follows. In section 2, 2 we first describe discuss the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics parameterization for ⟨Xmax⟩ and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their valuesσ(Xmax). In section 4, 3 we explain how test the hodoscope data are used to select specific muon geometries and how method with shower simulations assuming different mass distributions. Section 4 describes the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those application of the simulations and proceed method to study, in section 5, the detailed response data. The discussion of the WCD to muons, down to results and the level of single PMTsconclusions follow in sections 5 and 6 respectively. In section 6, we then present the result The details of the new measurement of parameterization and the scaling factor of best fit values for the calibration before concluding hadronic interaction models are summarized in section 7. 2020 2 Experimental setup‌appendix A.

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E& Oligosaccharides Advances in Stereoselective 1,2-mail: cis Glycosylation using C-2 Auxiliaries ▇▇▇▇ ▇▇_. ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the and ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate . ▇▇▇▇▇▇▇▇ (RPCs)*[a] Chem. Eur. J. 2017, enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison 23, 17637 – 17653 17637 T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Abstract: The control of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at stereoselectivity in a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on glycosylation reaction remains one of the WCDs, enables most challenging aspects of oli- gosaccharide synthesis. Especially the selection synthesis of single muons passing through 1,2-cis-gly- cosides is challenging and generally applicable methodology to prepare this linkage is needed to standardize oligosac- charide synthesis. This review highlights the detectorrecent develop- ment of an elegant strategy employing a C-2 auxiliary to control the anomeric stereoselectivity in glycosylations. The RPC segmentation allows us various auxiliaries developed to reconstruct muon trajectories date, their compatibility with protecting groups and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, monosaccharide types as well as the different acquisition configurations adopted and the data obtainedmechanistic aspects are summarized. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5Furthermore, the detailed response appli- cation, advantages and limitations of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding C-2 auxiliaries in section 7. 2020 2 Experimental setup‌oligo- saccharide synthesis are discussed.

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published Journal of Instrumentation Extraction of the muon signals recorded with the surface detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory using recurrent neural networks To cite this article: The ▇▇▇▇▇▇ ▇▇▇▇▇ collaboration et al 2021 JINST 16 P07016 View the article online for updates and enhancements. PUblisнeD by IOP Publishing for PUblisнing roR Sissa Medialab MeDialab ReceiveD: December 21, 2020 JINST AccepteD: March 19, 2021 PUblisнeD: July 12, 2021 2021 E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ AbstractJINST P07016 AbstRact: Extensive air showersThe ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, originating from ultraat present the largest cosmic-high energy cosmic raysray observatory ever built, have been suc- cessfully measured through the use is instrumented with a ground array of arrays of 1600 water-Cherenkov detectors detectors, known as the Surface Detector (WCDsSD). Sophisticated analyses exploiting WCD data have made The SD samples the secondary particle content (mostly photons, electrons, positrons and muons) of extensive air showers initiated by cosmic rays with energies ranging from 1017 eV up to more than 1020 eV. Measuring the independent contribution of the muon component to the total registered signal is crucial to enhance the capability of the Observatory to estimate the mass of the cosmic rays on an event-by-event basis. However, with the current design of the SD, it possible is difficult to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce straightforwardly separate the observed number contributions of muons at to the ground. The accurate knowledge SD time traces from those of the WCD response to muons is paramount in establishing the exact level of this discrepancyphotons, electrons and positrons. In this workpaper, we report on present a study method aimed at extracting the muon component of the response time traces registered with each individual detector of a WCD the SD using Recurrent Neural Networks. We derive the performances of the method by training the neural network on simulations, in which the muon and the electromagnetic components of the traces are known. We conclude this work showing the performance of this method on experimental data of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory Observatory. We find that our predictions agree with the parameterizations obtained by the AGASA collaboration to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of describe the lateral distributions of key observables between the hodoscope data electromagnetic and the predictions muonic components of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%extensive air showers. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 KeywordsKeywoRDs: Data reduction Analysis and statistical methods; Cherenkov detectors; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors Pattern recognition, cluster finding, calibration and fitting methods ⃝c 2020 2021 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/090221/16/07/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌P07016

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing Journal of Cosmology and Astroparticle Physics Search for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through photons with energies above 1018 eV using the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD hybrid detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate To cite this article: A. ▇▇▇ et al JCAP04(2017)009 You may also like - ATLAS data quality operations and performance for 2015–2018 data-taking G. ▇▇▇, ▇. Abbott, ▇.▇. ▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦et al. Comparison - Impact of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based atmospheric effects on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation reconstruction of UHECRs is performed indirectly by recording the extensive air showers produced observed by these particles when they interact in the atmosphere. At surface detectors of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing Journal of Cosmology and Astroparticle Physics Multi-resolution anisotropy studies of ultrahigh- Observatory To cite this article: ▇. ▇▇▇ et al JCAP06(2017)026 View the article online for Sissa Medialab 2020 JINST Eupdates and enhancements. You may also like - ATLAS data quality operations and performance for 2015–2018 data-mail: taking energy cosmic rays detected at the ▇▇▇▇▇_▇ ▇▇▇▇▇ ▇. ▇▇▇, ▇. ▇▇▇▇▇▇, ▇.▇. ▇▇▇▇▇▇ et al. - Impact of atmospheric effects on the energy reconstruction of air showers observed by the surface detectors of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. - Search for photons with energies above 1018 eV using the hybrid detector of the ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. ournal of Cosmology and Astroparticle Physics JCAP06(2017)026 Multi-resolution anisotropy studies of ultrahigh-energy cosmic rays detected at the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory The ▇▇▇▇▇▇ ▇▇▇▇▇ collaboration E-mail: auger ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showersReceived November 25, originating from ultra-high energy cosmic rays2016 Revised March 17, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations2017 Accepted May 26, based on different hadronic-interaction models2017 Published June 13, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌2017 −3

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use Journal of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge Cosmology and Astroparticle Physics Measurement of the WCD response to muons is paramount in establishing the exact level average shape of this discrepancy. In this work, we report on a study longitudinal profiles of the response of a WCD of cosmic-ray air showers at the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇To cite this article: A. ▇▇▇ (RPCs), enabling us to select et al JCAP03(2019)018 View the article online for updates and reconstruct nearly 600 thousand single muon trajectories enhancements. You may also like - Limits on point-like sources of ultra-high- energy neutrinos with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive Journal of Cosmology and Astroparticle Physics Observation of inclined EeV air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through showers with the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD radio detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇To cite this article: A. ▇▇▇ (RPCs), enabling us to select et al JCAP10(2018)026 View the article online for updates and reconstruct nearly 600 thousand single muon trajectories enhancements. You may also like - Limits on point-like sources of ultra-high- energy neutrinos with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing Journal of Instrumentation Antennas for Sissa Medialab 2020 JINST Ethe detection of radio emission pulses from cosmic-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive ray induced air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons showers at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 KeywordsTo cite this article: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude et al 2012 JINST 7 P10011 View the article online for updates and enhancements. You may also like - Test beam demonstration of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow silicon microstrip modules with transverse momentum discrimination for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the future CMS tracking detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive Journal of Cosmology and Astroparticle Physics Observation of inclined EeV air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through showers with the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD radio detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate To cite this article: ▇▇▇▇▇. ▇▇▇ (RPCs), enabling us to select et al JCAP10(2018)026 View the article online for updates and reconstruct nearly 600 thousand single muon trajectories enhancements. You may also like - Limits on point-like sources of ultra-high- energy neutrinos with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: Test Generation Based on Symbolic Specifications ▇▇▇▇ ▇▇▇▇▇_▇▇▇ , ▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇and ▇▇▇ ▇.▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate . ▇▇▇▇▇▇▇▇ (RPCs){lf, enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muonstretmans, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇}@▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇.▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays Abstract. Classical state-oriented testing approaches are based on sim- ple machine models such as Labelled Transition Systems (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the groundLTSs), in which the light produced data is represented by concrete values. To implement these theories, data types which have infinite universes have to be cut down to finite vari- ants, which are subsequently enumerated to fit in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs)model. The SD operates with a duty cycle close This leads to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size an explosion of the showersstate space. The shower size of all such events is subsequently converted into Moreover, exploiting the energy syntactical and/or semantical information of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectorsinvolved data types is non-trivial after enumeration. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purposeTo overcome these problems, we have designed and deployed a hodoscope composed lift the family of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down test- ing relations iocoF to the level of single PMTsSymbolic Transition Systems (STSs). In section 6We present an algorithm based on STSs, we then present which generates and executes tests on-the-fly on a given system. It is sound and complete for the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌iocoF testing relations.

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use Journal of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge Cosmology and Astroparticle Physics Measurement of the WCD response to muons is paramount in establishing the exact level average shape of this discrepancy. In this work, we report on a study longitudinal profiles of the response of a WCD of cosmic-ray air showers at the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate To cite this article: ▇▇▇▇▇. ▇▇▇ (RPCs), enabling us to select et al JCAP03(2019)018 View the article online for updates and reconstruct nearly 600 thousand single muon trajectories enhancements. You may also like - Limits on point-like sources of ultra-high- energy neutrinos with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Journal of Instrumentation Impact of atmospheric effects on the energy You may also like - ATLAS data quality operations and performance for 2015–2018 data-taking reconstruction of air showers observed by the ▇. ▇▇▇, ▇. ▇▇▇▇▇▇, ▇.▇. ▇▇▇▇▇▇ et al. - Search for photons with energies above surface detectors of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory To cite this article: ▇. ▇▇▇ et al 2017 JINST 12 P02006 1018 eV using the hybrid detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. - Muon counting using silicon photomultipliers in the AMIGA detector of the ▇▇▇▇▇▇ ▇▇▇▇▇ observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. View the article online for updates and enhancements. Published by IOP Publishing for Sissa Medialab 2020 2017 JINST E-mail: ▇▇▇▇▇_▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ P02006 Abstract: Extensive Atmospheric conditions, such as the pressure (P), temperature (T ) or air showersdensity ( ρ ∝ P/T ), originating from ultra-high energy affect the development of extended air showers initiated by energetic cosmic rays, have been suc- cessfully measured through . We study the use impact of the atmospheric variations on the reconstruction of air showers with data from the arrays of watersurface detectors of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, considering separately the one with detector spacings of 1500 m and the one with 750 m spacing. We observe modulations in the event rates that are due to the influence of the air density and pressure variations on the measured signals, from which the energy estimators are obtained. We show how the energy assignment can be corrected to account for such atmospheric effects. Keywords: Cherenkov detectors; Data analysis; Large detector systems for particle and astropar- ticle physics; Systematic effects ⃝c 2017 IOP Publishing Ltd and Sissa Medialab srl doi:10.1088/1748-Cherenkov detectors 0221/12/02/P02006 3 Determination of atmospheric coefficients from the modulations of the event rate 6 3.1 Results for the 1500 m array 7 3.2 Results for the 750 m array 10 2017 JINST 1 Introduction‌ P02006 Variation of the atmospheric conditions affect the signals from the extended air shower (WCDsEAS) which can be detected at ground level with arrays of surface detectors, such as the ones of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory. If these effects are not understood and properly accounted for, they can induce systematic effects in the energy reconstruction of the cosmic rays (CRs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulationsConsequently, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge determination of the WCD response to muons is paramount CR spectrum and also the search for anisotropies are affected, especially at large angular scales where the daily weather modulations can induce dipolar-like anisotropies in establishing the exact level distribution of this discrepancyarrival directions (although considering time periods of several years, partial cancellations of these modulations are expected). In this workan earlier investigation [1], we report on a study of studied the response of a WCD main effects due to changes in the atmospheric conditions using the data from the surface detector (SD) of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies end of August 2008. This included a total of about 106 events of all energies, with a median energy of about 0.6 EeV (where EeV ≡ 1018 eV). Results were interpreted based on theoretical models of shower development, validated with simulations of EAS in different atmospheric profiles. Those effects were already taken into account in the analyses of large scale anisotropies performed up to now [12]. Due In this work we improve and update the previous investigation by including events detected with a four times larger exposure. This enables us to restrict the very low flux dataset to events with energies above 1 EeV, which are less affected by trigger effects, allowing to quantify the atmospheric effects at these energiesthe energies which are used in most of the physics analyses. We also include data from the smaller but denser part of the array of detectors, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatorywith 750 m spacing, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited that was built after the passage completion of the charged particles1500 m array, allow for the observation which we consider events with energies above 0.1 EeV. The previous analysis is also improved by including a delay of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, about two hours in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial roleatmospheric temperature at the relevant heights (of about 500 m to 1 km above ground) with respect to the changes in the temperature measured at ground level. The objective of this work is to probe experimentally this simulation in terms This inertia of the atmospheric response turns out to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the be observable with our study of the signal response weather induced modulations of the WCD for different EAS signals, and is indeed also directly observed in the atmosphere (see the appendix). Finally, we obtain fits to the zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation angle dependence of the hodoscope allows us coefficients parameterising the weather induced modulations which are convenient to verify implement a component CR energy reconstruction corrected for the effects of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak variations in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muonsatmospheric conditions. 2 The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted surface detector arrays and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌sets‌ 2017 JINST P02006

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST EJournal of Cosmology and Astroparticle Physics Measurement of the average shape of longitudinal profiles of cosmic-mail: ray air showers at the ▇▇▇▇▇_▇ ▇▇▇▇▇ Observatory To cite this article: ▇. ▇▇▇ et al JCAP03(2019)018 View the article online for updates and enhancements. You may also like - Limits on point-like sources of ultra-high- energy neutrinos with the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. - Probing the origin of ultra-high-energy cosmic rays with neutrinos in the EeV energy range using the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. - Search for magnetically-induced signatures in the arrival directions of ultra- high-energy cosmic rays measured at the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory ▇. ▇▇▇, ▇. ▇▇▇▇▇, ▇. ▇▇▇▇▇▇▇▇ et al. ournal of Cosmology and Astroparticle Physics JCAP03(2019)018 E-mail: auger ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showersReceived November 13, originating from ultra-high energy cosmic rays2018 Accepted February 25, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations2019 Published March 7, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, located at an altitude of ∼1400 m above sea level near Malargüe in the province of ▇▇▇▇▇▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, extensive air showers are observed using two detection techniques. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage of the charged particles, allow for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector cannot be operated. 2020 JINST The detection and reconstruction of air showers allows not only for studies of the astrophysics of UHECRs, but also represents a unique opportunity to access particle interactions at energies that are far higher than could be achieved by any Earth-based accelerator. The number of muons in showers is particularly sensitive to hadronic interactions taking place during the development of the cascade in the atmosphere. Over the last 20 years, increasing numbers of studies (see [2] for a recent review), including the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications of a discrepancy between the number of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purpose, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ (RPCs), which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌2019

End User Agreement. This publication is distributed under the terms of Article 25fa of the Dutch Copyright Act. This article entitles the maker of a short scientific work funded either wholly or partially by Dutch public funds to make that work publicly available for no consideration following a reasonable period of time after the work was first published, provided that clear reference is made to the source of the first publication of the work. Research outputs of researchers employed by Dutch Universities that comply with the legal requirements of Article 25fa of the Dutch Copyright Act, are distributed online and free of cost or other barriers in institutional repositories. Research outputs are distributed six months after their first online publication in the original published version and with proper attribution to the source of the original publication. You are permitted to download and use the publication for personal purposes. All rights remain with the author(s) and/or copyrights owner(s) of this work. Any use of the publication other than authorised under this licence or copyright law is prohibited. If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the University Library know, stating your reasons. In case of a legitimate complaint, the University Library will, as a precaution, make the material inaccessible and/or remove it from the website. Please contact the University Library through email: ▇▇▇▇▇▇▇▇▇@▇▇▇.▇▇.▇▇. You will be contacted as soon as possible. University Library Radboud University Published by IOP Publishing for Sissa Medialab 2020 JINST E-mailArticle Multimedia Modeling of Engineered Nanoparticles with SimpleBox4nano: Model Definition and Evaluation ▇▇▇▇▇_▇▇▇ ▇. ▇. ▇▇▇▇▇▇▇▇▇▇▇▇▇@▇▇▇▇.▇▇▇ Abstract: Extensive air showers, originating from ultra-high energy cosmic rays, have been suc- cessfully measured through the use of arrays of water-Cherenkov detectors (WCDs). Sophisticated analyses exploiting WCD data have made it possible to demonstrate that shower simulations, based on different hadronic-interaction models, cannot reproduce the observed number of muons at the ground. The accurate knowledge of the WCD response to muons is paramount in establishing the exact level of this discrepancy. In this work, we report on a study of the response of a WCD of the ,*,† ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory to atmospheric muons performed with a hodoscope made of resistive plate . ▇▇▇▇▇▇▇▇ (RPCs), enabling us to select and reconstruct nearly 600 thousand single muon trajectories with zenith angles ranging from 0◦ to 55◦. Comparison of distributions of key observables between the hodoscope data and the predictions of dedicated simulations allows us to demonstrate the accu- racy of the latter at a level of 2%. As the WCD calibration is based on its response to atmospheric muons, the hodoscope data are also exploited to show the long-term stability of the procedure. P09002 Keywords: Data reduction methods; Large detector systems for particle and astroparticle physics; Large detector-systems performance; Performance of High Energy Physics Detectors ⃝c 2020 IOP Publishing Ltd and Sissa Medialab ▇▇▇▇▇://▇▇▇.▇▇▇/10.1088/1748-0221/15/09/P09002 2 Experimental setup 3 2.1 RPC hodoscope 3 2.2 DAQ and trigger 4 2.3 Acquisition campaigns 5 3 Simulation 6 3.1 Shower simulation 7 3.2 WCD simulation 8 3.3 RPC simulation 9 4 Data reconstruction and performances 9 4.1 Charge reconstruction with the WCD 9 4.2 Trajectory reconstruction with the RPC 10 4.3 Zenith angle and charge distributions 11 JINST P09002 2020 1 Introduction‌ The ▇▇▇,‡,§ Joris T. K. Quik,‡ A. ▇▇▇ ▇▇▇▇▇ Observatory▇▇▇▇,† and Dik van de Meent† †Institute for Water and Wetland Research, located Department of Environmental Science, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen, The Netherlands ‡Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands §IMARES − Institute for Marine Resources & Ecosystem Studies, Wageningen UR, P.O. Box 68, 1970 AB IJmuiden, The Netherlands *S Supporting Information ABSTRACT: Screening level models for environmental assessment of engineered nanoparticles (ENP) are not generally available. Here, we present SimpleBox4Nano (SB4N) as the first model of this type, assess its validity, and evaluate it by comparisons with a known material flow model. SB4N expresses ENP transport and concentrations in and across air, rain, surface waters, soil, and sediment, accounting for nanospecific processes such as aggregation, attachment, and dissolution. The model solves simultaneous mass balance equations (MBE) using simple matrix algebra. The MBEs link all concentrations and transfer processes using first-order rate constants for all processes known to be relevant for ENPs. The first-order rate constants are obtained from the literature. The output of SB4N is mass concentrations of ENPs as free dispersive species, heteroaggregates with natural colloids, and larger natural particles in each compartment in time and at steady state. Known scenario studies for Switzerland were used to demonstrate the impact of the transport processes included in SB4N on the prediction of environmental concentrations. We argue that SB4N- predicted environmental concentrations are useful as background concentrations in environmental risk assessment. ■ INTRODUCTION The nanotechnology industry is rapidly developing engineered nanoparticles (ENPs) that are applied in a great variety of consumer and industrial products.1 ENPs are designed to be nanoscaled (<100 nm) in at least two dimensions, so that nanospecific physicochemical properties emerge from the highly interfacial nature of the chemical material.2 This enables novel and unique applications in a wide spectrum of fields, such as electronics engineering, energy production, biomedical applications, food, agriculture, and many more.3 However, the specific properties of ENPs also raise concern about unforeseen environmental and toxicological consequences.4 There is thus a great need to evaluate the potential environmental risk of ENPs because release to the environment is considered to be inevitable.5 Current environmental risk management policies on chemical substances (e.g., the European Union’s chemical regulation REACH: Registration Evaluation Authorization and Restriction of Chemicals) have been designed for use with so- or nanocolloids.6 Making such adjustments is challenging because of the fundamental differences in transport- and transformation mechanisms between colloids and solutions.6−8 A major difficulty in making models for “conventional” chemicals fit for (nano)colloids is that hardly any field data are available to test the validity of nanoadjusted models.8,9 The adjustment is also an altitude urgent task, since products containing ENPs are already on the market. Previous attempts to model the environmental fate of ∼1400 m above sea level near Malargüe nanoparticles were meant to provide a first step in environmental exposure estimation of ENPs10,11 and are still too complex for direct implementation in chemical safety assessment frameworks.12 It has therefore been proposed to develop environmental risk assessment strategies with a pragmatic approach and using scientifically justified simplifica- tions.7 This paper is an attempt to aid in this approach by presenting a relatively simple environmental fate model that uses first- order kinetics to estimate environmental background concen- trations for nanocolloids in an environmental system that is called “conventional” chemicals, i.e., chemical substances in atomic/ionic or molecular forms, dissolved in water or in the province gas phase. However, regulatory procedures urgently need adjustment to become fit for application to the new nanochemicals that generally occur in solid forms, like micro- Received: January 31, 2014 Revised: April 7, 2014 Accepted: April 25, 2014 Figure 1. Overview of model concept SimpleBox4nano. composed of the compartments air, soil, water, and sediment that are represented as boxes: SimpleBox4nano (SB4N). A similar approach in modeling the fate of nanomaterials in air, water, and soil was recently published by ▇▇▇ and ▇▇▇▇▇.13 Unlike SB4N, ▇▇, Argentina, is the largest facility in the world dedicated to the detection of ultra- high energy cosmic rays (UHECRs) in the energy range from ∼1017 eV up to the highest energies [1]. Due to the very low flux at these energies, the observation of UHECRs is performed indirectly by recording the extensive air showers produced by these particles when they interact in the atmosphere. At the ▇ and ▇▇▇▇▇’▇ ▇▇▇▇▇ ObservatoryMendNano model assumes fixed (time independent) partitioning ratios for the processes of aggregation and attachment, extensive air showers which control the environmental fate of colloidal systems.8 In SB4N, these processes are observed modeled mechanistically using two detection techniquesfirst-order rate constants as will be explained in detail below. Telescopes collecting the fluorescence light emitted by atmospheric nitrogen, excited after the passage SB4N is a modified version of the charged particlesSimpleBox model, allow which has served as a regional distribution module in the European Union System for Evaluation of Substances (EUSES) model, used for exposure assessment in REACH.14−16 SB4N adds first- order rate constants for transport- and transformation processes of colloids, where the original SimpleBox model does so only for molecular processes of chemical substances dissolved in water.12 It has been identified that three major adaptations are necessary to make SimpleBox fit for ENPs:6 (1) transformation processes (e.g., from one colloidal form into another by homo- or heteroaggregation) should not be interpreted as removal processes; rather transformation products should be treated as altered species of the same ENP; (2) dissolution should be implemented as a removal mechanism and (3) thermodynamic equilibrium is not expected to be representative for the observation of the longitudinal profile of the showers. This technique provides a nearly calorimetric estimate of the energy carried by the primary particle. However, this technique is constrained to nights with low background light conditions, limiting its uptime to below 15%. The second detection technique uses a surface detector (SD) array composed of 1660 water-Cherenkov detectors (WCDs) deployed on the ground, in which the light produced actual concentrations in the water by charged particles above the threshold for emitting Cherenkov radiation is collected by three photomultiplier tubes (PMTs). environment, since ENPs generally form unstable colloidal systems.17 The SD operates with a duty cycle close to 100%. The detected signals in the SD are used to determine the arrival direction and to estimate the size latter implies that concen- tration ratios of the showers. The shower size of all such events is subsequently converted into the energy of the primary cosmic ray through a calibration based on a subset of events detected by both the surface and fluorescence detectors. This “hybrid” approach allows for a calorimetric estimate of the energy also for events recorded during periods when the fluorescence detector colloidal species cannot be operated. 2020 JINST calculated from equilibrium partitioning coefficients but must be modeled dynamically, as the result of forward and backward process rates.6 The detection and reconstruction of air showers allows not only for studies aim of the astrophysics present paper is to provide process formulations for modeling behavior of UHECRsENP and to evaluate its potential for use in environmental risk assessment. We explain how environmental concentrations can be calculated as a function of ENP emissions and ENP substance properties using colloidal and ultrafine particle theory. As existing theory which ENPs are taken up in aggregates or attach to the surfaces of larger particles, but also represents a unique opportunity and (4) the rates at which ENPs may be subjected to access particle interactions at energies that are far higher than could be achieved by any Earth-based acceleratorremoval processes such as degradation and dissolution. The number of muons in showers is particularly sensitive to hadronic interactions taking place during first-order rate constants are derived from formulations from the development of literature and are explained below (Supporting Information, eq 1 and Table 2). SB4N models the cascade in mass concentrations (mi/V = Ci) as state variables, using the atmosphere. Over the last 20 yearssame first-order rate constants (ki), increasing numbers of studies (see [2] written here for a recent review)one-compartment system, including for which the ▇▇▇▇▇▇ ▇▇▇▇▇ Observatory, have provided data showing indications time- dependent concentrations Ci(t) can be expressed analytically as the total mass mi present in an environmental compartment of a discrepancy between the number volume V at time t at constant emission Ei and removal ki for ENP species i:23 cannot exactly describe and predict environmental behavior of muons predicted in showers by different hadronic-interaction models and that observed in data. In Auger Observatory, the analyses developed in this context are based on the data from WCDs, from which a muon deficit has been revealed in simulations at energies around and above 1019 eV [3, 4]. P09002 In the comparison between the observed showers and showers predicted by models, the detailed simulation of the WCD, which includes all the relevant physics processes, accounts for the detector geometry, and simulates the response of the electronics, naturally plays a crucial role. The objective of this work is to probe experimentally this simulation in terms of the response to atmospheric particles, most notably background muons, at different zenith angles. For this purposem (t) ⎡ E ⎤ colloidal material under field conditions, we have designed and deployed a hodoscope composed of resistive-plate ▇▇▇▇▇▇▇▇ formulated C (RPCs)t) = i = ⎢ i (1 − e− ∑i kit)⎥ the model to be flexible, which, installed on one of the WCDs, enables the selection of single muons passing through the detector. The RPC segmentation allows us to reconstruct muon trajectories and impact points, thus enabling the study of the signal response of the WCD for different zenith angles (from 0◦ up to 55◦) of arriving muons and the comparison so that theoretically derived parameter values can be replaced with signals predicted by the detector simulation. In addition, the operation of the hodoscope allows us to verify a component of the WCD calibration procedure [5], which relies on the determination of the charge deposited by a vertical and centrally through-going atmospheric muon. As the WCD is not a directional detector, the peak experimentally determined ones in the charge distribution for vertical centered-muons is obtained by scaling the peak in the charge distribution obtained with the omni- directional muons. The latter is evaluated every minute for all data-taking WCDs, while the scaling factor was measured by means of a dedicated muon telescope on a reference WCD at the beginning of the operation of the Observatory [5, 6]. We took advantage of the RPC hodoscope to repeat with higher precision such a measurement and validate the scaling factor. Overall, two data acquisition campaigns took place with the RPC hodoscope: one to detect muons with more inclined zenith angles (up to 55◦) and the other dedicated to near-vertical muons. The presentation of the measurements, of the data analysis, and of the results is organised as follows. In section 2, we first describe the experimental setup, including a brief description of the features of the WCD, the RPC specifications, the related electronics and trigger system, as well as the different acquisition configurations adopted and the data obtained. The following section 3 illustrates the characteristics of the generated showers and the characteristics of the detector simulation. As for the latter, in appendix A we provide a list of the most relevant parameters and their values. In section 4, we explain how the hodoscope data are used to select specific muon geometries and how the associ- ated charge and trajectory are reconstructed. Then we show that the distributions of these basic ob- servables are comparable with those of the simulations and proceed to study, in section 5, the detailed response of the WCD to muons, down to the level of single PMTs. In section 6, we then present the result of the new measurement of the scaling factor of the calibration before concluding in section 7. 2020 2 Experimental setup‌V ⎢⎣ V ∑i ki ⎥⎦