Gamma/hadron discrimination at high energies through the azimuthal fluctuations of the particle distributions at ground

TL;DR

This paper introduces a new variable, LCm, that measures azimuthal non-uniformity in particle distributions at ground level to improve gamma/hadron discrimination in high-energy gamma-ray observatories, especially for energies from 10 TeV to 1 PeV.

Contribution

The paper presents a novel gamma/hadron discriminating variable, LCm, based on azimuthal fluctuations, enhancing background rejection in ground-array gamma-ray observatories.

Findings

LCm effectively distinguishes gamma from hadronic showers.

Discrimination power increases with array fill factor.

Results outperform traditional muon-based methods.

Abstract

Wide field-of-view gamma-ray observatories must fight the overwhelming cosmic ray background to identify very-high-energy astrophysical gamma-ray events. This work introduces a novel gamma/hadron discriminating variable, $LCm$, which quantifies the azimuthal non-uniformity of the particle distributions at the ground. This non-uniformity, due to the presence of hadronic sub-showers, is higher in proton-induced showers than in gamma showers. The discrimination power of this new variable is then discussed, as a function of the air shower array fill factor, in the energy range $10\,$TeV to $1\,$PeV, and compared to the classical gamma/hadron discriminator based on the measurement of the number of muons at the ground. The results obtained are extremely encouraging, paving the way for the use of the proposed quantity in present and future large ground-array gamma-ray observatories.