Contribution to construction and simulation of the CMS electromagnetic calorimeter at LHC

The CMS detector is one of the two general purpose experiments of the LHC (Large Hadron Collider). A major field of research at CMS is the search for the Higgs boson. At low luminosity the most promising signature for a light Higgs boson (< 150 GeV) is the di-photon decay. The LHC experimental environment is very difficult and the search of the Higgs boson for this channel requires an extremely precise electromagnetic calorimeter (ECAL) with fast response and high radiation hardness. In order to obtain this level of performance, beam tests were performed on several prototype of the calorimeter during the years 1999 and 2000. An important part of this thesis is dedicated to the analysis of the data taken in these tests. The main objective of this work is the study of the various parameters playing an essential role in the detector performances: - the energy resolution; - the crystals laser monitoring; - the performances of the front-end electronics in its quasi-final version. Another aspect of our work was to develop a highly realistic simulation of the ECAL barrel. This was done using the particle physics simulation tool GEANT and an interface (EUGENIE) between CAD designs and the simulation. This detector implementation was recently adopted by the CMS collaboration and included in the official simulation software. (author)