Identification of UHE photons for multi-messengers astronomy with universality at the Pierre Auger Observatory

Neutrinos, cosmic rays, photons of ultra high energy as well as gravitational waves provide complementary information to study the most energetic objects in the universe, allowing therefore the development of multi-messengers astronomy. The Pierre Auger Observatory is the current experiment studying cosmic rays at the highest energies and searching for the most energetic neutrinos and photons. The aim of the thesis work presented in this manuscript is to develop an efficient search of ultra high energy photons in the Auger data, by building a discriminating analysis based on a reconstruction method using the universality of extensive air showers. The observables used are obtained only from the surface detectors (SD) of the Observatory. The universality principle states that the average properties of air showers can be described by a small set of macroscopic parameters describing the air showers. A model predicting the signals in the detectors of the SD was developed by the collaboration. Thus, using this model, the maximum depth of the shower development, an observable not directly accessible with the SD, is reconstructed using the method developed in this thesis work. This observable allows to discriminate between photon-induced air showers and showers initiated by hadrons. The shower maximum being reconstructed, it is combined with two other variables describing the air showers, and they are implemented in a discriminating analysis. To begin with, the different steps of the analysis are developed and optimised on simulations of photon-induced and proton-induced showers. Then, its efficiency is studied on a sample of data detected by the Observatory and the results are compared to the current SD search for UHE photons. (author)