Recherche générique de nouvelle physique dans le canal eµ de l'expérience CMS du LHC

This work consists of a new physics search beyond the Standard Model using data collected by the CMS detector of the proton-proton collider LHC at CERN. This search focuses on a particular nal state : the electron-muon (eµ) channel. The data used have been recorded in 2012 at a center of mass energy √ s = 8 TeV with an integrated luminosity of L = 19.7 fb−1 . The analysis is based on an extra dimensions BSM (Beyond the Standard Model) scenario which predicts the existence of Z 0/γ0 bosons at masses of the order of a TeV. These bosons can decay into eµ pairs. Some of the Standard Model process can also give a eµ pair in the nal state, they form the background of this analysis. Top-antitop tt¯ and W+W− pair production are the two main backgrounds. Two events selection methods, Cut and count and multivariate analysis (MVA), have been studied and optimized in order to separate signal from background and maximize the S/√ B ratio. After having applied these methods to the data, the eµ mass spectrum is compatible with the Standard Model description and no peak is observed. A limit on the production cross section of any new physics particle times the eµ channel branching ratio is then set on the [200-1200] GeV/c2 range. Furthermore, the Cut and count method allows one to estimate the 95 % condence level exclusion limit of a Z 0/γ0 boson in the mass ranges [238-249] and [253-263] GeV/c2 . The very small number of expected signal events limits the sensitivity of the search and it would be benecial to conduct a similar search with the 2015-2016 CMS data in order to investigate the high mass region with better statistics.