The observation of a muon deficit in simulations from data of the Pierre Auger Observatory

Abstract

We present evidence from the Pierre Auger Observatory that the models currently used in simulation of cosmic ray air showers at the highest energies predict less muons than observed in data in the energy range around 1019 eV. We explain the different methods used to estimate the number of muons, apply them to observations, and compare the results to predictions from simulations of air showers. The number of muons in EAS derived from the observations of the Pierre Auger Observatory is a factor of 1.5 to 2.2 higher than that predicted in simulations. The exact discrepancy depends on the zenith angle and, to a lesser extent, on the hadronic interaction model and analysis technique.