Search for supersymmetric particles in opposite sign dilepton events with the CMS detector

A search for supersymmetric particles in the data collected by the CMS experiment at center of mass energy of 7 TeV is presented in this thesis . The analysis is focused on the selection of events with pairs of opposite sign electrons or muons. This particular exclusive signature (which we refer to as opposite sign dilepton signature) has a very good background rejection power and would allow systematic studies of the supersymmetric particles, once a sufficient amount of them is collected. The bulk of the analysis consists on the isolation of the events of new physics, through the performance of some selection cuts on properly chosen variables. Even if, after this step, most part of the standard model background is actually rejected, an estimate of the Standard Model events still surviving (mainly top pairs) is mandatory. The control of any residual background is here made using a particular data-driven method, involving many discriminating variables. With this technique, we are able to set exclusion limits in the cMSSM plane at 95% of confidence level, using a Bayesian approach.