A. Aab, Radboud University Nijmegen
P. Abreu, Instituto Superior Técnico
M. Aglietta, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
J. M. Albury, The University of Adelaide
I. Allekotte, Centro Atomico Bariloche
A. Almela, Universidad Nacional de San Martin
J. Alvarez Castillo, Universidad Nacional Autónoma de México
J. Alvarez-Muñiz, Universidad de Santiago de Compostela
G. A. Anastasi, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
L. Anchordoqui, Lehman College
B. Andrada, Universidad Nacional de San Martin
S. Andringa, Instituto Superior Técnico
C. Aramo, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
P. R. Araújo Ferreira, Rheinisch-Westfälische Technische Hochschule Aachen
H. Asorey, Universidad Nacional de San Martin
P. Assis, Instituto Superior Técnico
G. Avila, Pierre Auger Observatory
A. M. Badescu, University Politehnica of Bucharest
A. Bakalova, Institute of Physics of the Czech Academy of Sciences
A. Balaceanu, Horia Hulubei National Institute of Physics and Nuclear Engineering
F. Barbato, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
R. J. Barreira Luz, Instituto Superior Técnico
K. H. Becker, Bergische Universitat Wuppertal
J. A. Bellido, The University of Adelaide
C. Berat, Universite Grenoble Alpes
M. E. Bertaina, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
X. Bertou, Centro Atomico Bariloche
P. L. Biermann
T. Bister, Rheinisch-Westfälische Technische Hochschule Aachen
J. Biteau, Universite Paris-Saclay
A. Blanco, Instituto Superior Técnico
J. Blazek, Institute of Physics of the Czech Academy of Sciences
B. Fick, Michigan Technological UniversityFollow
D. F. Nitz, Michigan Technological UniversityFollow
A. Puyleart, Michigan Technological University

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Department of Physics


The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between 2 × 10 17 and 2 × 10 18 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at 1017.5eV and 1018eV. We find that, for the models to explain the data, an increase in the muon density of 38 % ± 4 % (12 %) ±18%21% for EPOS-LHC, and of 50 % (53 %) ± 4 % (13 %) ±20%23% for QGSJetII-04, is respectively needed.

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Publication Title

European Physical Journal C

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.


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