"Explosive regime" should dominate collisions of ultra-high energy cosmic rays

TL;DR

This paper suggests that at ultra-high energies, cosmic ray collisions enter an explosive regime with collective phenomena similar to heavy ion collisions, significantly affecting secondary particle spectra and cosmic ray cascade development.

Contribution

It introduces the idea that ultra-high energy cosmic ray collisions exhibit collective behaviors akin to heavy ion collisions, which was not previously considered at such energies.

Findings

Velocity of transverse expansion comparable to LHC PbPb collisions

Transition from fluctuation-dominated to collective regime at E_lab ~ 10^{20} eV

Implications for cosmic ray cascade spectra

Abstract

Since the launch of LHC experiments it has been discovered that the high multiplicity trigger in pp, pA collisions finds events behaving differently from the typical (minimally biased) ones. In central pPb case it has been proven that those possess collective phenomena known as the radial, elliptic and triangular flows, similar to what is known in heavy ion (AA) collisions. In this paper we argue that at the ultra-high energies, E_lab ~ 10^{20} eV, of the observed cosmic rays this regime changes from a small-probability fluctuation to a dominant one. We estimate velocity of the transverse collective expansion for the light-light and heavy-light collisions, and find it comparable to what is observed at LHC for the central PbPb case. We argue that significant changes of spectra of various secondaries associated with this phenomenon should be important for the development of the cosmic ray cascades.