Hadronic interactions at ultra high energies -- tests with the Pierre Auger Observatory

TL;DR

This paper reports on measurements from the Pierre Auger Observatory that test hadronic interaction models at ultra-high energies, revealing discrepancies in muon predictions and highlighting the need for improved models.

Contribution

First direct estimation of proton-proton cross-section at 55 TeV using cosmic ray data, challenging existing hadronic interaction models extrapolated from LHC energies.

Findings

Models underestimate muon numbers at ground level.

Electromagnetic component measurements are consistent with expectations.

Discrepancies suggest the need for revised hadronic interaction models.

Abstract

The Pierre Auger Observatory is a hybrid detector for cosmic rays with E > 1EeV. From the gathered data we estimated the proton-proton cross-section at sqrt(s) = 55 TeV and tested other features of the hadronic interaction models, which use extrapolations from the LHC energy. The electromagnetic component, carrying most of the energy of the shower, is precisely measured using fluorescence telescopes, while the hadronic back- bone of the shower is indirectly tested by measuring the muons arriving to the surface detector. The analyses show that models fail to describe these two components consistently, predicting too few muons at the ground.