A study of photon-jets and their identification variables computed in the electromagnetic calorimeter of an in-house, ATLAS-like, detector model developed at Uppsala University for full-simulations is presented. The signal, which is based on the Composite Higgs Model, considers the pair production of vector-like top quarks, denoted t', with the successive decays t' to S and a Standard Model top quark and S to two photons, where S is a new pseudo-scalar boson. For clustering purposes, Topological Clustering was implemented and compared against the already implemented Sliding Window clustering algorithm. A modification to the Topological Clustering algorithm used in the ATLAS detector was made and compared against the original version. The performance test showed a significant mass reconstruction improvement with Topological Clustering. Furthermore, the performance test showed some improvement with the modifications in the Topological Clustering for photons in a collimated scenario. The signal is compared to Standard Model background consisting of one photon plus zero, one or two jets, and isolated photons from the Higgs boson decaying into two photons. Even though some discrimination could be found, the analysis showed that standard cut and count strategy won't work and hence, further analysis with machine learning should be tested.

La première partie de cette thèse est dédiée à l’extraction des corrections de l’échelle en énergie des jets dans l’expérience CMS du LHC. Les diverses méthodes d’extraction sont détaillées, en insistant tout particulièrement sur l’utilisation des événements photon + jets. Les corrections ainsi extraites sont primordiales pour les analyses de physique utilisant des jets, et sont d’ores et déjà utilisées par toute la collaboration.La deuxième partie présente la recherche de physique au-delà du Modèle Standard dans le secteur du quark top. De nombreux modèles de nouvelle physique prédisent en effet de nouvelles particules, pouvant se manifester comme des résonances dans le spectre de masse top-antitop. Deux analyses sont présentées dans cette thèse, une dédiée à la recherche des résonances de spin 1 et une dédiée à la recherche de résonances de spin 0, où les phénomènes d’interférences avec le Modèle Standard sont pris en compte / The first part of this thesis is dedicated to the extraction of jet energy scale corrections for the CMS experiment at the LHC. Various extraction methods are described, with a particular interest on corrections extraction using photon + jets events. These corrections are necessary for all analyses using jets and are already used by the whole collaboration. The second part presents the searches for new physics beyond the Standard Model. Many models of new physics predict new particles with enhanced coupling to the top quark, which can show up as resonances in the top-antitop invariant mass spectrum. Two separate analyses are described in this thesis, one dedicated to the search of spin 1 resonances and one dedicated to the search of spin 0 resonances, where interference effects with the Standard Model production are taken into account