Recent results from the Pierre Auger Observatory on the mass composition and hadronic interactions of ultra-high energy cosmic rays

Alexey Yushkov,B Pattison

doi:10.1051/epjconf/201614505002

Abstract

Recent results on the mass composition and hadronic interactions of ultra-high energy cosmic rays (UHECR) obtained at the Pierre Auger Observatory are reviewed. Different studies based on shower observables recorded with the fluorescence and surface detectors of the Observatory indicate that the mass composition is getting lighter for the energies below ≈ 2 EeV and heavier afterwards. A fully consistent description of the data collected at the Observatory cannot be achieved with any of the up-to-date interaction models.

Highlights

A large variety of data, with unprecedented statistics, has been collected at the Pierre Auger Observatory [1] since the start of the operation in 2004
The approaches relying on the studies of the EM component or using general properties of the extensive air showers have smaller uncertainties due to hadronic interaction models compared to the approaches making use of absolute values related to the muon component
Three of the analyses presented below – measurements of the depth of shower maximum Xmax, of the correlation between Xmaxand signal in water-Cherenkov detectors (WCD), and of the muon content in highly inclined events – exploit the advantages of the hybrid design of the Observatory

Summary

Introduction

A large variety of data, with unprecedented statistics, has been collected at the Pierre Auger Observatory [1] since the start of the operation in 2004. The approaches relying on the studies of the EM component (analysis of the depth of the shower maximum Xmax) or using general properties of the extensive air showers (analysis of the correlation between Xmaxand the signal in surface stations or studies of the elongation rates) have smaller uncertainties due to hadronic interaction models compared to the approaches making use of absolute values related to the muon component. In this proceedings the results on the mass composition from the first and second types of the methods are compared and the conclusions on both the evolution of the primary mass with energy and on the drawbacks of the interaction models (EPOS-LHC [2], QGSJetII-04 [3], Sibyll 2.1 [4]) are presented.

Xmax using the relation

Distributions of

Discussion

EPOS LHC