Recherche de résonance lourde dans le spectre de masse invariante top-antitop auprès de l'expérience ATLAS du LHC

This report presents the analysis conducted with the ATLAS experiment at the LHC and searching for resonnant production of new particles decaying into a pair of top quarks. Top quark reconstruction is mainly build upon the notion of hadronic jets, whose identification and reconstruction is a crucial issue for any measure trying to sign top quark decays from proton-proton collisions processes. After a general description of the theoretical and experimental features of jet reconstruction in the ATLAS detector, we present a first attempt to validate the local hadronic calibration method, which aim at correcting the measurement of these objects from inaccuracies caused by detector effects. In the second part, we present the analysis conducted on 14~fb−1 of proton-proton collision data at sqrts=8~TeV collected during the year 2012 and searching for resonnant creation of new extit{heavy} particles in top-antitop invariant mass spectrum. For heavy particles, the quarks produced in the decay of the latter have a high impulsion with respect to their mass and those top quark decays often results in a so called og boosted fg topology, where the hadronically decaying top quark is often reconstructed as a single jet of large radius parameter. In this context, we present a preliminary study to reconstruct and identify as precisely as possible this type of boosted topologies, based on the study of jet substructure.