Discrepancies in the Monte Carlo simulations of propagation of ultra-high energy cosmic-ray photons in the geomagnetic field

TL;DR

This paper compares two Monte Carlo simulation programs, PRESHOWER and MaGICS, highlighting discrepancies in modeling ultra-high energy cosmic-ray photon propagation in the geomagnetic field, which is crucial for accurate air shower predictions.

Contribution

It identifies and analyzes discrepancies between the two main Monte Carlo codes used for simulating preshower effects of ultra-high energy photons in the geomagnetic field.

Findings

Discrepancies found between PRESHOWER and MaGICS simulations.

Differences impact the modeling of photon interactions above 10^19 eV.

Results emphasize need for standardization in simulation tools.

Abstract

The discrepancies in the results produced by the two most commonly used Monte Carlo programs for simulation of propagation of ultra-high energy cosmic ray photons in the presence of the geomagnetic field are presented. Although photons have not yet been discovered in the cosmic ray flux at highest energies, the capabilities of the present cosmic ray detectors make their discovery possible, according to the predictions of conventional models, within the next few years. It is therefore necessary to have a reliable and well maintained software for relevant simulations. The results of this paper are important for simulations of propagation of photons at energies above 10^19 eV. Photons of such high energies might interact with the geomagnetic field giving rise to a cascade of particles even above the atmosphere. This effect is called a "preshower effect". The preshower effect is important for air shower evolution and has to be accounted for in full Monte Carlo simulations of propagation of highest energy cosmic-ray photons. In this paper we compare the two most frequently used Monte Carlo codes for preshower simulations: PRESHOWER, used as a stand-alone program or as a part of CORSIKA, and MaGICS, used as a part of AIRES.