Recherche de technicouleur avec l'expérience ATLAS. Développement d'outils et étude des performances du calorimètre à argon liquide.

In 2011 the LHC has provided almost 5 fb-1 of data to the experiments. These data have been used to perform a deep commissioning of the detectors, understand the performances of the detector and perform physics analysis. This thesis is organized in five chapter. The first one is a theoretical introduction to the Standard Model and to one of its possible extension: the TechniColor. The second chapter gives a brief overview of the LHC and the ATLAS experiments. In the third chapter one of the key subsystem of the ATLAS experiment is presented: the LAr calorimeters. The monitoring of the data acquisition developed during my thesis is also presented in this chapter. The fourth chapter presents a study of the jet performances based on the data set acquired in 2010. This study has shown that in 2010, the Monte Carlo was underestimating the jet energy resolution by a relative factor of about $10\%$. This study was refocused to evaluate the impact of the reduced LAr HV area on the jet energy resolution. The impact of the HV reduced region was found to be negligible. For jets produced with a rapidity $|y|<0.8$, the increase of energy resolution due to the HV reduction, is evaluated at less than $3\%$ for a $p_{T}=30~GeV$ jet, and less than $0.1\%$ for a $p_{T}=500~GeV$ jet. Finally the last chapter of this thesis present a study of the $W\gamma$ final state. The standard model backgrounds contributing to this final state were estimated from Monte Carlo and from data. A search for narrow resonances was then conducted using the M($W\gamma$) distribution in a range [220,440]~GeV, but no significant deviation from the SM was observed. This study has allowed to set limits on the production of TC particles corresponding to $M(a_{T})>265\,GeV$ or $M(\rho_{T})>243\,GeV$.