Proton-proton interactions at the Highest Energies: the Grey-Disk and the Core-Corona models

TL;DR

This paper combines Grey-Disk and Core-Corona models to explain features of ultra-high-energy cosmic ray interactions, suggesting a proton-dominated spectrum from extragalactic sources with implications for cosmic ray composition.

Contribution

It introduces a novel combined model scenario that accounts for observed cosmic ray features and discusses its consistency with various observational data.

Findings

Explains $X_{max}$ and $N_bc$ distributions at highest energies.

Proposes a proton-dominated cosmic ray spectrum from extragalactic sources.

Suggests significant implications for understanding UHECR sources and composition.

Abstract

In this letter, the Grey-Disk and the Core-Corona models are combined in a scenario that aims to explain different unexpected features observed in the interactions of the highest energy particles in the Earth's atmosphere. In particular, the observed distributions of $X_{\rm max}$ and $N_\mu$ are explained, assuming that the ultra-high-energy cosmic ray spectrum is dominated by protons produced by a few extra-galactic sources with different injection spectra and maximum energy cutoffs. The compliance of this heterodox scenario with other relevant observations as the instep region in the energy spectrum, the event-by-event correlations between $X_{\rm max}$ and the detected signal at the ground and the absence of detection, so far, of UHE neutrinos or photons, are also briefly discussed. If confirmed, such a scenario would dramatically change the present understanding of the UHECR primary composition and, thus, the characteristics of their sources.