Search for Physics Beyond the Standard Model in the Opposite-Sign Same-Flavor Dilepton Final State with the CMS Detector

The Standard Model of particle physics has been remarkably successful in describing results of generations of collider and fixed-target experiments. Despitethe model’s success, many open questions remain; an extension will be necessaryat the very least at the Planck scale, where quantum gravity must be incorporatedinto the theory. An excellent candidate for a possible extension of the StandardModel is supersymmetry, which predicts a partner particle for each particle of theStandard Model and solves several of the shortcomings of the Standard Model.In this thesis, a search for supersymmetry in the final state with two opposite-signsame-flavor leptons, jets, and missing transverse energy is presented. This finalstate is very common in scenarios of physics beyond the Standard Model, andmany models contain decay chains producing correlated lepton pairs and thereforefeature a kinematic edge in the dilepton mass distribution. The present searchuses 19.4 fb−1 of√integrated luminosity of proton-proton collisions at a center-ofmass energy of s = 8 TeV, collected by the Compact Muon Solenoid detectorat CERN’s Large Hadron Collider. Two different approaches are used: a countingexperiment at low invariant dilepton mass to detect a generic same-flavor signal,and a fit in a broader dilepton mass range to find a kinematic edge. The search isperformed separately for central leptons (i.e. lepton pairs where both leptons arein the barrel region) and non-central leptons (where at least one of the leptons isoutside the barrel region). The dominating background consists of flavor symmetric processes, i.e. processes which produce same-flavor and opposite-flavor leptonpairs with equal probability. Smaller contributions arise from Z + jets events, nonprompt leptons, and rare backgrounds. The backgrounds are predicted using data