Test du modèle du "Petit Higgs" dans ATLAS au LHC, et simulation de la numérisation du calorimètre électromagnétique

LHC is a proton-proton collider with an energy of 14 TeV in the center of mass, which will start in 2007 at CERN. Two of its experiments, ATLAS, and CMS, will search and study in particular the Higgs boson, Supersymmetry and other new Physics. This thesis was about two aspects of the ATLAS experiment : â on one hand the simulation of the liquid Argon electromagnetic calorimeter, with the emulation of the electronic chain in charge of the digitization of the signal and also the evaluation of the electronic noise and the pile-up noise (coming from minimum bias events at LHC). These two points have been validated by the analysis of the data taken during beam tests in 2002 and 2004. â on the other hand, a physics study concerning the Little Higgs model. This recent model solves the hierarchy problem of the Standard Model, in introducing new heavy particles to cancel quadratic divergences arising in the calculation of the Higgs boson mass. These new particles, with a mass about the TeV/c2, are one heavy quark top, heavy gauge bosons ZH, WH and AH, and a heavy Higgs bosons triplet. The physics study dealt with the characteristic decays of the model, ZH->Z+H and WH->W+H, with a Higgs mass either at 120 GeV/c2 decaying in two photons or at 200 GeV/c2 decaying in ZZ or WW. Results show that in both cases, for 300fbâˆ'1 (3 years at high luminosity), an observation of the signal at 5 sigma for ZH et WH masses less than 2 TeV/c2 is possible, covering a large part of the parameter space.