Towards Gamma-Ray Astronomy at ultra-high energies

N. GONZALEZ; F. SANCHEZ ET AL

Otro; Publicación interna Pierre Auger (GAP 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-energyphotons, it is crucial to define composition-sensitive parameters capable of adequatelyrejecting the hadronic background. In this work, we explore the parameter Mb that combines the muon densities measured by the AMIGA buried scintillation detectors and theirdistance to the shower core, similarly to the well-known observable Sb. We analyze thediscrimination power of Mb between photon and proton primaries in the energy rangebetween EMC = 10^16.5 eV and EMC = 10^17.5 eV. The aim of this work is to tune Mb tobe applied in the 433 m Infill array (AERAlet) whose central station is equipped with aburied scintillation detector. We found that Mb with b = 2 can separate photons fromprotons via the number of muons in the nearest muon detector with a merit factor ofat least ∼ 5.06 at energies around Erec = 10 17 eV. By imposing a cut on the value ofM2 = 0.065, 99.90% of the background (proton) events can be rejected at a 1σ confi-dence level while keeping 79.8% of the photon events for energies above E rec = 10^16.5 eVfollowing a realistic spectrum. These are quite encouraging results.