Tests of hadronic interactions using the Pierre Auger Observatory
August 02, 2019
Ultra-high energy cosmic rays (UHECR) can be used to study hadronic interactions beyond LHC energies. In
this contribution, we summarize relevant data from the Pierre Auger Observatory.
While the proton-air cross section has been measured at $\sqrt s = 57$ TeV and found to be in good agreement
with extrapolations from LHC energies, other observables are significantly different from what is predicted using
current models. In particular, the predictions from models of showers based on LHC data are in strong contradiction
with the observed number of muons. More muons are detected than predicted with the magnitude
of the effect being model-dependent. Another observable from the Pierre Auger Observatory, the distribution of the
depths of muon production, is also poorly described. Indeed no current model is capable of describing the full
range of data from the Observatory, thus highlighting deficiencies in extrapolations beyond LHC energies.
The discrepancy between hadronic models can be examined further by measuring separately the muon and
electromagnetic components of the signal recorded by detectors on the ground. The Pierre Auger Observatory is
being upgraded by the addition of plastic scintillator detectors above the water-Cherenkov detectors to achieve this.
The new observations will enable rigorous testing of hadronic models up to $\sqrt s \sim 100$ TeV and are crucial
to the quest of determining the composition of UHECR.
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