Abstract : The quest for the Higgs boson, is one of the mains goals of the CMS detector, which will be operated at the next proton-proton collider LHC. In this thesis, the electromagnetic calorimeter is involved.
In the first part of this thesis the ECAL performance is evaluated with the data taken during the 2003 beam tests. The choices concerning the electronics readout have been made.
The second part uses the ECAL in order to evaluate the discovery potential of the Higgs boson in the associated production channel: if the Higgs boson mass is between 115 and 150 GeV/c^2, its decay into two photons may be detected. it is produced in association with a W or Z boson. The W and Z decay into electrons or muons. The charged tracks of these leptons allow the unambiguous reconstruction of the interaction vertex and a good mass resolution. This signal, and the numerous backgrounds have been simulated and reconstructed. The data analysis allows to confirm the existence of a light Higgs boson in the Standar Model framework. Analysis considering the MSSM is also performed.