Optimisation des critères d'identification des électrons et recherche de Supersymétrie dans les canaux avec deux leptons de même charge à partir des données du détecteur ATLAS

The LHC collisions center of mass energy rose up to 13 TeV in 2015, strongly increasing the production cross sections of hypothetical heavy particles (for example by a factor 50 for pair production of gluinos with a 1.5 TeV mass) and thus, paving the way for new physics searches. An optimisation of the electron identification criteria and a search for Supersymmetry with the ATLAS detector data were performed in this context. The first part is dedicated to the definition and the expected performance of the electron identification used for the trigger and the analysis of the 2015 data. The methodology defined to adapt these criteria to the experimental constraints is detailed. The second part is dedicated to the search for strongly produced supersymmetric particles in events with two same sign leptons (electrons or muons), jets and missing transverse energy using the full 2015 dataset (3.2 fb−1 at √s = 13 TeV). The main aspects of the analysis are described, paying particular attention to the experimental background. As no significant excess over the Standard Model expectation is observed, the results are interpreted using several simplified models to set limits on the masses of the gluinos, the squarks and the neutralinos. For instance, gluino masses up to 1.1 TeV are excluded, which represents an improvement of about 150 GeV with respect to the previous limits for some models with compressed mass spectra.