Le calorimètre électromagnétique de CMS pour la recherche du boson de Higgs $H \to ZZ^(*) \to 4e$ au LHC.

The work presented in this thesis has been carried out within the CMS (Compact Muon Solenoid) collaboration. CMS is one of the four experiments that will be installed at the LHC (Large Hadron Collider) at CERN. The thesis if focused on the electromagnetic calorimeter of CMS. The performance of the calorimeter is studied in detail using test beam data as well as a full simulation of the complete detector. The electronic noise in the readout chain is analyzed, and two methods to reconstruct the signal amplitude are proposed, one for signals that saturate the readout electronics while the other is intended to be used in case of noise in the readout chain. The thesis also presents a study of the electron reconstruction in CMS. This study has brought to the first definition of the "quality" measu! rement of an electron in CMS, to establish a procedure to esta! blish th e energy scale measurement of the electrons and to combine the information of calorimetry and tracking to have the best estimate of the electron quadri-momentum at vertex. The results of these studies are applied to the analysis of the Higgs decay channel H->ZZ(*)->4e for which both a standard sequential selection strategy and an optimized neural network technique are proposed.