Supersymmetry Searches in Dilepton Final States with the ATLAS Experiment

One of the main goals of the ATLAS experiment at the Large Hadr on Collider (LHC) at CERN in Geneva is the search for new physics beyond the Standa rd Model. In 2011, proton- proton collisions were performed at the LHC at a center of mas s energy of 7 TeV and an in- tegrated luminosity of 4 . 7 fb − 1 was recorded. This dataset can be tested for one of the most promising theories beyond limits achieved thus far: supers ymmetry. Final states in supersym- metry events at the LHC contain highly energetic jets and siz eable missing transverse energy. The additional requirement of events with highly energetic leptons simplifies the control of the backgrounds. This work presents results of a search for supe rsymmetry in the inclusive dilepton channel. Special emphasis is put on the search within the Gau ge-Mediated Symmetry Breaking (GMSB) scenario in which the supersymmetry breaking is medi ated via gauge fields. Statis- tically independent Control Regions for the dominant Stand ard Model backgrounds as well as Signal Regions for a discovery of a possible supersymmetry s ignal are defined and optimized. A simultaneous fit of the background normalizations in the Con trol Regions via the profile like- lihood method allows for a precise prediction of the backgro unds in the Signal Regions and thus increases the sensitivity to several supersymmetry mo dels. Systematic uncertainties on the background prediction are constrained via the jet multi plicity distribution in the Control Regions driven by data. The observed data are consistent wit h the Standard Model expectation. New limits within the GMSB and the minimal Supergravity (mSU GRA) scenario as well as for several simplified supersymmetry models are set or extended