Remarks on the chemical composition of highest-energy cosmic rays

TL;DR

This paper discusses the conflicting results on the chemical composition of the highest-energy cosmic rays, suggesting that observed variations may not be due to changes in primary cosmic ray nuclei.

Contribution

It offers a reinterpretation of Auger and HiRes data, proposing that composition changes are not the sole explanation for observed shower maximum fluctuations.

Findings

Auger and HiRes results can be reconciled without assuming composition change

Shower maximum fluctuations may not directly indicate primary cosmic ray composition

Energy dependence of shower maxima does not necessarily imply nuclear composition variation

Abstract

We present arguments aiming to reconcile the apparently contradictory results concerning the chemical composition of cosmic rays of highest energy, coming recently from Auger and HiRes collaborations. In particular, we argue that the energy dependence of the mean value and root mean square fluctuation of shower maxima distributions observed by the Auger experiment are not necessarily caused by the change of nuclear composition of primary cosmic rays.