Search for SUSY in Same-Sign Di-LeptonEvents with the CMS Detector

In this thesis a search for new physics is presented, based on events with two isolated same sign leptons (muons and electrons), jets, and missing transverse energy. The analyzed data corresponds to an integrated luminosity of 1.1 fb$^{-1}$ and is collected with the CMSdetector in proton-proton collisions at the LHC with a center-of-mass energy of 7TeV. A counting experiment is established by developing an event selection in order to selectsignal events in three dierent channels $(\mu\mu, e\mu, and ee)$, while rejecting the Standard Model background as eciently as possible. Standard Model background contributionsare classied into several categories and estimated using dierent techniques. A total of7 events is observed in data, being in agreement with the Standard Model backgroundprediction of 11$\pm$1(stat.)$\pm$2.7(syst.) events. Hence, no evidence for new physics is found.The observations are utilized to constrain the cMSSM by setting upper exclusion limitson possible signal contributions. The technical part of this theses contributes to the planned upgrade of the CMS experiment, by giving a motivation for a certain readout design of the hadronic calorimeter, inorder to improve the performance of the detector in future