New developments in data-driven background determinations for SUSY searches in ATLAS

The LHC will open a whole new window on supersymmetry (SUSY) searches, probing energies where also the Standard Model (SM) behavior is unknown. To find evidence for physics beyond the SM like SUSY, the first challenge is to understand the backgrounds from SM processes at high energy. To this end we present a method that determines the background using as little information from Monte Carlo simulation as possible. We construct three-dimensional models for the three main backgrounds. These models are created such that known and understood physics features, like a top or W mass peak, are incorporated. We parametrize these models, and fit them to our data set. By floating the shape parameters in the models, we minimize our dependence on the Monte Carlo information. We can show that this method can determine the composition of the background accurately. By fitting to the data in a control (sideband) region, with low S/B, and extrapolating to a region with high S/B, we can reliably predict the expected number of background events in the signal region, and determine the significance when an excess caused by SUSY events would be found. We can show that this method works even when SUSY events contaminate the control region.