Towards Gamma-Ray Astronomy at ultra-high energies

N. GONZÁLEZ, F. SÁNCHEZ, M. ROTH, A. ALMELA, B. ANDRADA, A. M. BOTTI, A. CANCIO, A. ETCHEGOYEN, L. FERREYRO, J. M. FIGUEIRA, B. GARCÍA, E. HOLT, J. HULSMAN; F. SUAREZ; A. LUCERO, D. MELO, S. MÜLLER, M. PERLIN, M. PLATINO, D. RAVIGNANI, D. SCHMIDT, G. SILLI, A. TABOADA, O. WAINBERG, B. WUNDHEILER, M. RONCORONI, E. SANTOS, C. SARMIENTO-CANO, A. YUSHKOV

Otro; Pierre Auger Internal Technical Note; 2017

The Auger Observatory has a unique possibility of exploring a new branch of Astron- omy: Gamma Astronomy at the highest energies. In the search for ultra-high-energy photons, it is crucial to define composition-sensitive parameters capable of adequately rejecting the hadronic background. In this work, we explore the parameter Mb that com- bines the muon densities measured by the AMIGA buried scintillation detectors and their distance to the shower core, similarly to the well-known observable Sb. We analyze the discrimination power of Mb between photon and proton primaries in the energy range between EMC = 10^16.5 eV and EMC = 10^17.5 eV. The aim of this work is to tune Mb to be applied in the 433 m Infill array (AERAlet) whose central station is equipped with a buried scintillation detector. We found that Mb with b = 2 can separate photons from protons via the number of muons in the nearest muon detector with a merit factor of at least ∼ 5.06 at energies around Erec = 10^17 eV. By imposing a cut on the value of M2 = 0.065, 99.90% of the background (proton) events can be rejected at a 1 sigma confi- dence level while keeping 79.8% of the photon events for energies above Erec = 10^16.5 eV following a realistic spectrum. These are quite encouraging results