Etude de la recherche du boson de higgs en deux photons dans l'experience atlas au lhc et calibration du calorimetre a argon liquide

The physics program of the ATLAS experiment at the Large Hadron Collider (CERN) covers a wide area going from the search for a Standard Model Higgs boson to the search for new physics (supersymetry, extra-dimensions...). This thesis focuses on two main axes : First, some studies on the liquid argon calorimeter electronics are presented. Studies related to the search for the Standard Model Higgs boson in the Higgs to two photons decay channel (which is one of the most promising discovery channels in the low mass region, between the LEP limit m_H>144.4 GeV and 150 GeV) are also detailed. In particular the reconstruction of photons and the use of photons conversion into electron-positron pair are detailed. The aim of these studies is to increase the discovery potential of the Higgs boson. Aspects related to the validation of the fast simulation package of the ATLAS experiment are also discussed: The performances of the photon reconstruction (for both unconverted and converted photons) as well as the ability to reproduce full simulation results are emphasized.