Mass Composition of UHECRs from $X_{\max }$ Distributions Recorded by the Pierre Auger and Telescope Array Observatories

Abstract

In this paper we infer the mass composition of the ultra high energy cosmic rays (UHECRs) from measurements of $X_{\max }$ distributions recorded at the Pierre Auger (2014) and Telescope Array (TA) (2016) Observatories, by fitting them with all possible combinations of Monte Carlo (MC) templates from a large set of primary species (p, He, C, N, O, Ne, Si and Fe), as predicted by EPOS-LHC, QGSJETII-04 and Sibyll 2.1 hadronic interaction models. We use the individual fractions of nuclei reconstructed from one experiment in each energy interval to build equivalent MC $X_{\max }$ distributions, which we compare with the experimental $X_{\max }$ distributions of the other experiment, applying different statistical tests of compatibility. The results obtained from both experiments confirm that the mass composition of the UHECRs is dominated ($\gtrsim$$70\%$) by protons and He nuclei {in the energy range investigated $\lg E(\mathrm{eV})$ = [17.8--19.3] (Auger) and $\lg E(\mathrm{eV})$ = [18.2--19.0] (TA).} The indirect comparisons between the $X_{\max }$ distributions recorded by the two experiments show that the degree of compatibility of the two datasets is good, even excellent in some high energy intervals, especially above the ankle ($\lg E(\mathrm{eV})\sim 18.7$). However, our study reveals that, at low energies, further effort in data analysis is required in order to harmonize the results of the two experiments.

Published in Universe

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Cited by in corpus (5)

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• Learning the Composition of Ultra High Energy Cosmic Rays
• Fermi acceleration under Lorentz invariance violation
• Bose-Einstein condensation and muon production in ultra-high energy cosmic ray particle collisions
• UHECRs Propagation and their Multimessengers: Upper limits and the Impact of the Extragalactic Magnetic Field