MAXIMUM MUON PRODUCTION DEPTH AND ITS FLUCTUATIONS ABOVE 15 EEV AT THE PIERRE AUGER OBSERVATORY: MASS COMPOSITION AND CONSTRAINTS ON HADRONIC INTERACTION MODELS

The surface detector array of the Pierre Auger Observatory measures the arrival time distribution of particles and it therefore provides indirect information on the longitudinal development of the muonic component of extensive air showers. In this work, the depth at which the muon production is maximum and the corresponding shower-to-shower fluctuations are reconstructed for more than 2000 events above 15 EeV (1.5X10^19 eV), in a wide range of zenith angles between 45° and 65°. Both observables are analysed in terms of mass composition of ultra-high energy cosmic rays, one of the most intriguing issues of modern astrophysics. In addition, these observables are exploited to attempt to constrain the most up-to date hadronic interactions models, which are used in the simulation of extensive air showers.