Search for ultra-high energy photons: observing the preshower effect with gamma-ray telescopes

TL;DR

This paper explores using gamma-ray telescopes to detect air showers caused by ultra-high energy photons affected by the preshower effect, aiming to improve photon identification and understand phenomena like the GZK effect.

Contribution

It introduces a novel method of detecting ultra-high energy photons via cosmic-ray ensembles and employs machine learning for improved separation from hadronic backgrounds.

Findings

Simulations show detectable air showers from CRE induced by ultra-high energy photons.

Boosted decision trees enhance separation of cosmic-ray ensembles from hadronic events.

Predicted event rates vary based on photon production models.

Abstract

Ultra-high energy photons constitute one of the most important pieces of the astroparticle physics problems. Their observation may provide new insight on several phenomena such as supermassive particle annihilation or the GZK effect. Because of the absence of any significant photon identification by a leading experiments such as the Pierre Auger Observatory, we consider a screening phenomenon called preshower effect which could efficiently affect ultra-high energy photon propagation. This effect is a consequence of photon interactions with the geomagnetic field and results in large electromagnetic cascade of particles several thousands kilometers above the atmosphere. This collection of particles, called cosmic-ray ensembles (CRE), may reach the atmosphere and produce the well-known air showers. In this paper we propose to use gamma-ray telescopes to look for air showers induced by CRE. Possible sources of ultra-high energy photons include the GZK effect and Super Heavy Dark Matter particles. Simulations involving the preshower effect and detectors response are performed and properties of these peculiar air showers are investigated. The use of boosted decision trees to obtain the best cosmic-ray ensemble/hadron separation, the aperture and event rate predictions for a few models of photon production are also presented.