Improving photon-hadron discrimination based on cosmic ray surface detector data

TL;DR

This paper explores optimizing the surface parameter Sb to improve photon-hadron discrimination in cosmic ray detectors, aiming to enhance photon detection limits at ultra-high energies.

Contribution

It introduces an optimized use of the surface parameter Sb for better photon-hadron discrimination in cosmic ray surface detectors at EeV energies.

Findings

Sb can be optimized for photon-hadron discrimination.

Array geometry and muon component modeling affect discrimination performance.

Discrimination efficiency varies with primary energy and zenith angle.

Abstract

The search for photons at EeV energies and beyond has considerable astrophysical interest and will remain one of the key challenges for ultra-high energy cosmic ray (UHECR) observatories in the near future. Several upper limits to the photon flux have been established since no photon has been unambiguously observed up to now. An improvement in the reconstruction efficiency of the photon showers and/or better discrimination tools are needed to improve these limits apart from an increase in statistics. Following this direction, we analyze in this work the ability of the surface parameter Sb, originally proposed for hadron discrimination, for photon search. Semi-analytical and numerical studies are performed in order to optimize Sb for the discrimination of photons from a proton background in the energy range from 10^18.5 to 10^19.6 eV. Although not shown explicitly, the same analysis has been performed for Fe nuclei and the corresponding results are discussed when appropriate. The effects of different array geometries and the underestimation of the muon component in the shower simulations are analyzed, as well as the Sb dependence on primary energy and zenith angle.