Early SUSY Searches at the CMS Experiment at CERN

When the Large Hadron Collider (LHC) commences operation, physicists all over the world will be eagerly awaiting data. The LHC was built as a discovery machine and the two general purpose detectors ATLAS and CMS might see evidence for new ndings with the rst year of data. Among the possible early discoveries is supersymmetry or SUSY. For SUSY events there exist irreducible backgrounds - Standard Model processes that are in principle indistinguishable from the signal. A possible search channel for SUSY are events with jets + one lepton + large missing transverse energy or 6ET . In this channel there also exists a signi cant contribution of Standard Model top anti-top production. For early data the prediction of the background overshadowing the expected supersymmetric events by computer simulations is subject to large uncertainties. It is necessary to use strategies that estimate the background in the signal region by using information from regions that are expected to be signal-free. The work examines such techniques for data based background estimates, based on the ABCD method. The predictive power is analyzed statistically, possible pitfalls and methods to evade them are given. In addition, the robustness of one of the central discriminating observables - 6ET - is studied, comparing two reconstruction techniques.