Identification of Gamma Ultra High Energy Cosmic Rays by Simulating Extensive Air Showers

Among the most interesting tasks for the identification of Ultra High Energy Cosmic Rays (origin, mechanisms of acceleration, top down model, direction, and maximum energy) is their isotopic composition. For example, if they are protons, heavier nuclei, gammas or even exotic. Air Shower Extended Simulation code (AIRES) is used to simulate the Extended Atmospheric Showers. This code gives, among others, the maximum number of secondary particles within the atmosphere along the longitudinal direction of the showers. From the distribution of the depths of maximum number of shower particles and their content in muons, we can distinguish between proton and gamma primary cosmic rays, both of energy of 100 EeV. The results show a maximum at lower atmospheric depths for protons and at higher for gammas, respectively. Due to the bremsstrahlung and pair production effects, the muon content of gamma showers is much poorer than of protons. Both facts enable the distinction between proton and gamma cosmic rays. For the simulation of the atmospheric EAS due to the passage of an Ultra High Energy Cosmic Ray, the Linsley standard atmospheric model is used.