Impact of QCD jets and heavy-quark production in cosmic-ray proton atmospheric showers up to 10$^{20}$ eV

TL;DR

This study integrates PYTHIA 6 with atmospheric shower simulations to explore how heavy-quark production and jet dynamics influence cosmic-ray induced air showers up to 10^20 eV, revealing differences from traditional models.

Contribution

First implementation of PYTHIA 6 with atmospheric shower simulation, highlighting the impact of jet and heavy-quark production on EAS properties compared to standard cosmic-ray models.

Findings

PYTHIA predicts more muonic activity at large distances from the shower axis.

EAS characteristics with PYTHIA are intermediate between other models.

Heavy-quark production has limited effect on muon properties, suggesting nuclear effects are key.

Abstract

The PYTHIA 6 Monte Carlo (MC) event generator, commonly used in collider physics, is interfaced for the first time with a fast transport simulation of a hydrogen atmosphere, with the same density as air, in order to study the properties of extended atmospheric showers (EAS) produced by cosmic ray protons with energies E$_{CR}\approx 10^{14}$--$10^{20}$ eV. At variance with the hadronic MC generators (EPOS-LHC, QGSJET, and SIBYLL) commonly used in cosmic-rays physics, PYTHIA includes the generation of harder hadronic jets and heavy (charm and bottom) quarks, thereby producing higher transverse momentum final particles, that could explain several anomalies observed in the data. The electromagnetic, hadronic, and muonic properties of EAS generated with various settings of PYTHIA 6, tuned to proton-proton data measured at the LHC, are compared to those from EPOS-LHC, QGSJET 01, QGSJET II, and SIBYLL 2.1. Despite their different underlying parton dynamics, the characteristics of the EAS generated with PYTHIA 6 are in between those predicted by the rest of MC generators. The only exceptions are the muonic components at large transverse distances from the shower axis, where PYTHIA predicts more activity than the rest of the models. Heavy-quark production, as implemented in this study for a hydrogen atmosphere, does not seem to play a key role in the EAS muon properties, pointing to nuclear effects as responsible of the muon anomalies observed in the air-shower data.