Towards Gamma Ray Astronomy at ultra high energies

NICOLÁS GONZÁLEZ; FEDERICO SÁNCHEZ; MARKUS ROTH; ALEJANDRO ALMELA; MARÍA BELÉN ANDRADA; ANA MARTINA BOTTI; ANGEL CANCIO; LUCIANO FERREYRO; JUAN MANUEL FIGUEIRA; ALAN FUSTER; BEATRIZ GARCÍA; MATÍAS ROLF HAMPEL; EWA HOLT; JOHANNES HULSMAN; MARIELA JOSEBACHUILI; AGUSTÍN LUCERO; DIEGO MELO; SARAH MÜLLER; MATIAS PERLIN; MANUEL PLATINO; DIEGO RAVIGNANI; MATÍAS RONCORONI; EVA SANTOS; CHRISTIAN SARMIENTO-CANO; DAVID SCHMIDT; GAIA SILLI; FEDERICO SUÁREZ; ÁLVARO TABOADA; OSCAR WAINBERG; BRIAN WUNDHEILER; ALEXEY YUSHKOV; ALBERTO ETCHEGOYEN

Otro; Pierre Auger Collaboration internal note; 2017

The Auger Observatory has a unique possibility of exploring a new branch of Astronomy: 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 combines 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= 1016.5eV and EMC= 1017.5eV. 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= 10^17eV. By imposing a cut on the value of M2= 0.065, 99.90% of the background (proton) events can be rejected at a 1sigma confidence 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.