Résultats des tests en faisceau sur les bouchons du calorimètre électromagnétique d'ATLAS - Séparation électrons-jets.

ATLAS is one of the four experiments being built on the future proton-proton collider at CERN : the LHC. This experiment has a large physics program, from Standard Model to new physics. The search for the Higgs boson in two photons or in four leptons, or the search of Z' or W' needs a good energy resolution for the electromagnetic calorimeter. This thesis describes the beam tests performed on three modules of the electromagnetic end cap calorimeter. A 0.6% non-uniformity, and a 0.7% energy resolution global constant term (dominant at high energy) has been obtained. Moreover, a study on the separation between electrons and jets is also performed. This study shows that a jets rejection factor of 10 5 105 can be obtained keeping an electron efficiency better than 78%.