Recherche de quarks vectoriels produits par l'échange de gluons lourds dans le cadre de modèles de Higgs composite avec le détecteur ATLAS
Being the missing piece of the Standard Model (SM) for decades, the Higgs boson was finally observed by the ATLAS experiment in 2012. Despite this discovery, it is justified to think that the SM is an effective theory at low energy scale, and one of the physics goal of the ATLAS experiment is to understand the origin of the electroweak symmetry breaking which the SM fails to explain. The technical and logistic challenges necessary for such a discovery makes the ATLAS detector one of the most sophisticated apparatus in the world. As a multipurpose detector, the ATLAS detector is built to investigate physics Beyond the SM and discover new particles. Composite Higgs models (CHM) are extensions to the SM that shed light on some problems left open, such as the mass hierarchy problem. Composite Higgs models also predict the existence of new particles such as vector-like quarks (VLQs). As one the simplest extension to the SM particle content VLQs are actively search for at the LHC.  This thesis presents the results obtained in the search for the single production of VLQs $\BH$ of charge $-1/3$ through the exchange of a heavy gluon $G^*$. Based on a simplified minimal CHM, the search is performed for the process $pp \to G^* \to \BH\bar b/\bar B_\text{H}b \to H\bbbar \to \bbbar\bbbar$. The dataset corresponds to 19.5~$\fb$ of $pp$ collisions at a centre-of-mass energy of $\sqrt s = 8$~TeV. No significant excess of events with respect to SM predictions is observed. Therefore upper limits on the cross section times branching ratio are set. Using a specific benchmark model, a lower limit of 2.0~TeV on the $G^*$ mass is obtained when $\mg = 2\mb$.
LHC ATLAS VLQ 8 TeV Composite Higgs Mass hierarchy problem Vector-like quarks Heavy gluon Single production