Supersymmetry Search in Multilepton Final States with Taus Using the CMS Detector at the LHC

This dissertation presents a search for SUperSYmmetry (SUSY) in multilepton final states with a data set corresponding to 34.9 pb−1 collected in 2010 with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) running at a center-of-mass energy of 7 TeV. The analysis channels contain combinations of at least three leptons: electrons, muons, and hadronically decaying taus that are reconstructed using a particle-flow technique. The minimal SUperGRAvity (mSUGRA) model and co-Next-to-the-Lightest-SUSY-Particle (co-NLSP) scenario in the Gauge-Mediated SUSY Breaking (GMSB) model are considered. To identify SUSY signal events, signal and Standard Model (SM) background processes are studied with full detector simulation and systematics uncertainties are evaluated. Relevant SM backgrounds include Z boson + jets, diboson, tt, and QCD processes. The separation between the signal and background is performed using a cut-based selection. Good agreement between simulated samples and data is obtained, in particular for the significant Z boson + jets background. With the chosen event selection, we observe three events in data, consistent with the SM predic- tion within statistical fluctuations. Therefore, we set exclusion limits on both models using Bayesian statistics. For the SUSY parameters of m0 = 60 GeV, A0 = 0, tanβ = 3, and μ > 0, chargino masses below 163 GeV are excluded in the mSUGRA model. In GMSB, gluino masses up to 1040 GeV are excluded in co-NLSP scenario.