Measuring the muon content of inclined air showers using AERA and the water-Cherenkov detectors of the Pierre Auger Observatory

We present a novel approach for assessing the muon content of air showers with large zenith angles on a combined analysis of their radio emission and particle footprint. We use the radiation energy reconstructed by the Auger engineering radio array (AERA) as an energy estimator and determine the muon number independently with the water-Cherenkov detector array of the Pierre Auger Observatory, deployed on a 1500 m grid. We focus our analysis on air showers with primary energy above 4 EeV to ensure full detection efficiency. Over approximately ten years of accumulated data, we identify a set of 40 high-quality events that are used in the analysis. The estimated muon contents in data are compatible with those for iron primaries as predicted by current-generation hadronic interaction models. This result can be interpreted as a deficit of muons in simulations as a lighter mass composition has been established from <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>X</a:mi> <a:mi>max</a:mi> </a:msub> </a:math> measurements. This muon deficit was already observed in previous analyses of the Auger Collaboration and is confirmed using hybrid events that include radio measurements for the first time.

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Journal
Physical review. D/Physical review. D.
Published
2025-10-31
DOI
https://doi.org/10.1103/2q9f-pbrp
Primary Topic
Astrophysics and Cosmic Phenomena
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article
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article

Measuring the muon content of inclined air showers using AERA and the water-Cherenkov detectors of the Pierre Auger Observatory

Karl J. Friston
Physical review. D/Physical review. D.
Astrophysics and Cosmic Phenomena
article

Measuring the muon content of inclined air showers using AERA and the water-Cherenkov detectors of the Pierre Auger Observatory

Karl J. Friston
article en

Abstract

We present a novel approach for assessing the muon content of air showers with large zenith angles on a combined analysis of their radio emission and particle footprint. We use the radiation energy reconstructed by the Auger engineering radio array (AERA) as an energy estimator and determine the muon number independently with the water-Cherenkov detector array of the Pierre Auger Observatory, deployed on a 1500 m grid. We focus our analysis on air showers with primary energy above 4 EeV to ensure full detection efficiency. Over approximately ten years of accumulated data, we identify a set of 40 high-quality events that are used in the analysis. The estimated muon contents in data are compatible with those for iron primaries as predicted by current-generation hadronic interaction models. This result can be interpreted as a deficit of muons in simulations as a lighter mass composition has been established from <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>X</a:mi> <a:mi>max</a:mi> </a:msub> </a:math> measurements. This muon deficit was already observed in previous analyses of the Auger Collaboration and is confirmed using hybrid events that include radio measurements for the first time.

Physical review. D/Physical review. D.Vol. 112(12)
Karlsruhe Institute of Technology (DE), Universidad Industrial de Santander (CO), University of Rome Tor Vergata (IT), Michigan Technological University (US), Universidade Federal do Rio de Janeiro (BR), National Technological University (AR), Université Libre de Bruxelles (BE), Vrije Universiteit Brussel (BE), University of Lisbon (PT), University of Salento (IT), Radboud University Nijmegen (NL), Consejo Nacional de Investigaciones Científicas y Técnicas (AR), Federal Center for Technological Education Celso Suckow da Fonseca (BR), Universität Hamburg (DE), University of Wuppertal (DE), Colorado School of Mines (US), Universidad de Granada (ES), Universidad Michoacana de San Nicolás de Hidalgo (MX), City University of New York (US), Universidade de São Paulo (BR), Universidade Estadual de Campinas (UNICAMP) (BR), University of Milan (IT), University of Nova Gorica (SI), Universidade de Santiago de Compostela (ES), Université Paris Cité (FR), University of Siegen (DE), Charles University (CZ), Universidade Estadual de Feira de Santana (BR), Universidad de Buenos Aires (AR), University of L'Aquila (IT), Université Paris-Saclay (FR), Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso (IT), Folkwang University of the Arts (DE), Balseiro Institute (AR), Bariloche Atomic Centre (AR), Jožef Stefan Institute (SI), University of Łódź (PL), University of Catania (IT), University of Chicago (US), Universidade Federal de Campina Grande (BR), Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering (RO), National Institute for Subatomic Physics (NL), Institute of Nuclear Physics (UZ), Osservatorio Astrofisico di Torino (IT), Institute of Scientific and Technical Research for Defense (AR), FZU ‒ Institute of Physics of the Academy of Sciences of the Czech Republic (CZ), Centro Brasileiro de Pesquisas Físicas (BR), Universidad de Medellín (CO), Universidad Autónoma de Chiapas (MX), Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo (IT), Institute of Physics Rosario (AR), Instituto de Tecnologías en Detección y Astropartículas (AR), Universidad Nacional Tecnológica (DO), Institute of Space Science - INFLPR Subsidiary (RO), Institute of Astronomy and Space Physics (AR), Gran Sasso Science Institute (IT), Pierre Auger Observatory (AR), International Center for Advanced Studies (AR), Universidade Federal do Paraná (BR), University of Turin (IT), The University of Adelaide (AU), New York University (US), Case Western Reserve University (US), Instituto Politécnico Nacional (MX), Palacký University Olomouc (CZ), University of Naples Federico II (IT), Universidade Federal do ABC (BR), Benemérita Universidad Autónoma de Puebla (MX), University of Delaware (US), Vrije Universiteit Amsterdam (NL), Universidad Nacional de La Plata (AR), University of Amsterdam (NL), RWTH Aachen University (DE), Universidad Nacional Autónoma de México (MX), Université Grenoble Alpes (FR), University of Palermo (IT), Netherlands Institute for Radio Astronomy (NL), Comisión Nacional de Energía Atómica (AR), Politecnico di Milano (IT)
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