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Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - CRI - Cosmic Ray Indirect
Searching for UHE photons in the EeV range: a two-variable approach exploiting air-shower universality.
P. Savina,* C. Bleve, L. Perrone
*corresponding author
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Pre-published on: 2019 July 22
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The signatures of a photon-induced air shower are a larger atmospheric depth at the shower maximum ($X_\text{max}$) and a lower number of muons with respect to the bulk of hadron-induced background. Hybrid experiments combining a fluorescence detector (FD) and a ground array of particle detectors (SD) can measure $X_\text{max}$, energy ($E$) and the geometry of the shower with high precision. The muonic content is usually estimated through mass-sensitive SD observables that have a complex dependence on the shower geometry, $E$ and $X_\text{max}$. We present here a method to simplify this approach using the paradigm of universality. Air-shower universality models the average contribution of different secondary particles starting from a limited number of parameters such as $E$, $X_\text{max}$, the muonic content and the geometrical configuration of the shower axis relative to the detector. We describe a method to derive a parameter, $R_{\mu}$, directly related to the muonic content using the total signal recorded in individual detectors of a ground array. The approach is tested on full air shower simulations using as a case study the array of water-Cherenkov detectors of the Pierre Auger Observatory.
The technique is explored in terms of photon/hadron separation capability over the energy range between 1 and 30 EeV. We show how the combination of $R_{\mu}$ and $X_\text{max}$, in the case of hybrid detection, can lead to a strong hadron/photon separation power even when the number of triggered stations at the ground is limited.
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