Speaker
Description
In this paper we infer the mass composition of the ultra high energy cosmic rays (UHECRs) from measurements of $X_{\rm max}$ 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 $X_{\rm max}$ distributions which we compare with the experimental $X_{\rm max}$ distributions of the other experiment, applying different statistical tests of compatibility: Kolmogorov - Smirnov ($KS$), Anderson – Darling ($AD$) and $p-value$ as goodness of fit.
The results obtained from both experiments confirm that the mass composition of the UHECRs is dominated ($\gt 70\%$) by protons and He nuclei on the entire energy spectrum. The indirect comparisons between the $X_{\rm max}$ distributions recorded by the two experiments show that the two data sets are not compatible to each other on the entire energy range $\lg E (\rm eV) = [18.2 - 19.0]$. We obtain very low probabilities of compatibility ($< 10^{-5}$) especially at lower energies but becoming increasingly large around and above the \textit{ankle} ($\lg E (\rm eV) \sim 18.7$), obtaining excellent agreement in some high energy intervals.
Keywords
"mass composition; fitting fractions of $X_{max}$ distributions"
| Subcategory | Experimental Methods & Instrumentation |
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