Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory

A Aab, Universität Siegen, Fachbereich 7 Physik-Experimentelle Teilchenphysik, Germany.
P Abreu, Laboratório de Instrumentação e Física Experimental de Partículas-LIP and Instituto Superior Técnico-IST, Universidade de Lisboa-UL, Portugal.
M Aglietta, Osservatorio Astrofisico di Torino (INAF), Torino, Italy.
E J. Ahn, Fermi National Accelerator Laboratory, Batavia, Illinois, USA.
I Al Samarai, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Universités Paris 6 et Paris 7, CNRS-IN2P3, France.
I F. Albuquerque, Universidade de São Paulo, Inst. de Física, São Paulo, Brazil.
I Allekotte, Centro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET), Argentina.
J D. Allen, New York University, New York, New York, USA.
P Allison, Ohio State University, Columbus, Ohio, USA.
A Almela, Instituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Argentina.
J Alvarez Castillo, Universidad Nacional Autónoma de México, Mexico.
J Alvarez-Muñiz, Universidad de Santiago de Compostela, Spain.
M Ambrosio, INFN, Sezione di Napoli, Italy.
G A. Anastasi, INFN, Sezione di L'Aquila, Italy.
L Anchordoqui, Department of Physics and Astronomy, Lehman College, City University of New York, Bronx, New York, USA.
B Andrada, Instituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica, Argentina.
S Andringa, Laboratório de Instrumentação e Física Experimental de Partículas-LIP and Instituto Superior Técnico-IST, Universidade de Lisboa-UL, Portugal.
C Aramo, INFN, Sezione di Napoli, Italy.
F Arqueros, Universidad Complutense de Madrid, Spain.
N Arsene, University of Bucharest, Physics Department, Romania.
H Asorey, Centro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET), Argentina.
P Assis, Laboratório de Instrumentação e Física Experimental de Partículas-LIP and Instituto Superior Técnico-IST, Universidade de Lisboa-UL, Portugal.
J Aublin, Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Universités Paris 6 et Paris 7, CNRS-IN2P3, France.
G Avila, Observatorio Pierre Auger, Argentina.
A M. Badescu, University Politehnica of Bucharest, Romania.
C Baus, Karlsruhe Institute of Technology, Institut für Experimentelle Kernphysik (IEKP), Germany.
J J. Beatty, Ohio State University, Columbus, Ohio, USA.
K H. Becker, Bergische Universität Wuppertal, Department of Physics, Germany, Germany.
J A. Bellido, University of Adelaide, Australia.
C Berat, Laboratoire de Physique Subatomique et de Cosmologie (LPSC), Université Grenoble-Alpes, CNRS/IN2P3, France.
M E. Bertaina, INFN, Sezione di Torino, Italy.
X Bertou, Centro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET), Argentina.
P L. Biermann, Max-Planck-Institut für Radioastronomie, Bonn, Germany.

Abstract

Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_{CM}=110-170 TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory. The average hadronic shower is 1.33±0.16 (1.61±0.21) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons.