The Mass of Cosmic Rays of Ultra High Energy
arXiv:2508.11378
Abstract
A review of several analyses is presented that forces the conclusion that the mass composition of the highest-energy cosmic rays is not proton-dominated. This deduction, combined with the use of a modern hadronic interaction model, should lead to a re-evaluation of the energy spectrum reported by the Telescope Collaboration that may well bring that measurement, and the corresponding one from the Pierre Auger Observatory, into better agreement.
Revised version. Minor revision after refereeing. Accepted for publication in Astroparticle Physics April 2026