A Muon-based Observable to Detect Photons at Ultra-high Energies

F. SANCHEZ (VER ADJUNTO)

Madison

Conferencia; 36th International Cosmic Ray Conference (ICRC 2019); 2019

University of Madison

The observation of an ultra-high energy photon component in the cosmic radiation is one ofthe open problems in Astroparticle Physics. The stringent theoretical and experimental upperlimits to the photon flux above 100 TeV make the search of a weak photon signal in the vasthadronic cosmic ray background a challenging task. At these energies, photon primaries enteringthe atmosphere develop an extensive air shower which is driven by electromagnetic processes witha poor muon production. The muon content is one of the most promising observables leadingto the discrimination between photons and hadronic cosmic rays. In this article, we define aparameter capable of quantifying the muon component while reducing the fluctuations due to theunknown lateral distribution of muons. We explain the different features of this observable usingsimulated air showers between 30 and 300 PeV. We show that a merit factor of 5 in the separationbetween photon and proton primaries and a signal efficiency of at least ∼ 92% while rejecting99.97% of the background can be reached considering realistic resolution effects on the showerfeatures.