Calorimeter-Based Triggers at the ATLAS Detector for Searches for Supersymmetry in Zero-Lepton Final States

摘要

This thesis consists of three closely related parts. An analysis of datarecorded by the ATLAS detector in 2010 in proton-proton collisions at acenter-of-mass energy of 7 TeV with an integrated luminosity of 33.4/pb isperformed, searching for supersymmetric final states containing jets andmissing transverse energy and no electrons or muons (zero-lepton channel). Noexcess over the Standard Model background expectation is observed. Using theCLs and PLR methods, exclusion limits are set in two different supergravitymodels. These considerably extend the excluded parameter ranges from earlierexperiments. The rates and efficiencies of triggers based on combined signatures with jetsplus missing transverse energy in ATLAS are studied, which are the primarytriggers for the search for Supersymmetry in the zero-lepton channel. For themeasurement of the efficiencies in data collected in 2010 and 2011, thebootstrap method is applied. Different sample triggers based on jets andmissing transverse energy are compared and their efficiencies are measured. Areweighting approach is used to correct for the bias from the propagation ofthe uncertainties in the bootstrap method. A universal model is developed to describe the contribution of fake missingtransverse energy from resolution effects to the rates of missing transverseenergy triggers as function of the level of in-time pile-up, i.e. the number ofconcurrent proton-proton interactions. The input parameters are tuned to theproperties of the ATLAS trigger system, and the model predictions are comparedto measurements of trigger rates in ATLAS. Good agreement is found for lowthresholds for which the rates are dominated by resolution effects, whereas therates for higher thresholds are underestimated due to additional sources offake and real missing transverse energy, which are not incorporated in themodel.