Etudes dans le canal avec deux leptons de même signe de la physique du top au-delà du Modèle Standard

The central subject of this thesis is the search for new physics in which the top quark plays a crucial role. The LHC is a proton collider, designed for a nominal operation with sqrt(s) = 14 TeV. Until december 2011 it worked with an energy of 7 TeV in the center of mass. The first 5 f b−1 of collected data allowed us to constrain some parameters of the new physics processes presented in this thesis. The document is divided into three parts : The first one describes briefly the LHC accelerator before presenting the ATLAS experiment and operation of the detector. The Tower Builder Boards for the electromagnetic level one trigger are especially studied. The second part is a phenomenological analysis of physics beyond the Standard Model with four top quarks in the final state. This analysis is presented for several theoretical models. This study was performed mainly at the generator level for sqrt(s) = 14 TeV but we also comments on prospects at 7 TeV. It can be applied to both ATLAS and CMS experiments. The third part is an experimental study, performed with the ATLAS detector, searching for two exotic processes with two same signe leptons in the final state (T5/3 and four tops production). A limit on the mass of the top partner T5/3 has been obtained as well as a limit on the cross section of exotic events with four tops.