Study of the linearity of the Electromagnetic Calorimeter of the Compact Muon Solenoid experiment using $J/\Psi$, $\Upsilon$ and $Z$ resonances

The work is divided into four chapters. In the first chapter the Standard Model is introduced, together with a short introduction on the Weak interactions and the Higgs theory. The Higgs boson main production and decay channels are presented, as well as the state of the art concerning its mass measurements. In the second chapter the LHC accelerator is briefly presented and the CMS experiment is described, focusing on the characteristics of its electromagnetic calorimeter ECAL, which is crucial for the identifications and measurements of the electrons in the four leptons Higgs decay channel. In the third chapter the algorithms for the electron energy reconstruction are presented. The various detector calibration methods are considered as well. In the fourth chapter the fine-tuning of the ECAL energy scale are presented together with the study of the residual non-linearity. The correction function to be applied to the electron energy from the decay of simulated Higgs boson events are derived and the systematic uncertainty on its reconstructed mass is evaluated.