Search for Electroweak SUSY Signatures with Two Leptons and Missing Energy with the ATLAS Detector

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Ueno, Ryuichi




The ATLAS experiment at the Large Hadron Collider (LHC) has collected significant amounts of proton-proton (pp) collision data from 2010 until 2012. These data have allowed the discovery of a new boson consistent with the one postulated by the Higgs' theory, and also enabled to look for hints of new physics beyond the Standard Model (SM). Supersymmetry (SUSY) is an extension of the SM that introduces a symmetry between fermions and bosons. Its signatures are expected to be detectable at the LHC, should it be the true extension to the SM, and the ATLAS experiment offers a dedicated programme to search for such signatures. This thesis presents the analysis and results for the search for SUSY produced from electroweak interactions resulting in two final-state leptons and some missing energy. The full 2012 dataset is used for the analysis, corresponding to 20.3 fb^{-1} of pp collisions at the centre-of-mass energy of \sqrt{s} = 8 TeV. The overall methodology to identify these SUSY signatures is given, with emphasis on the optimization of the SUSY discovery signal region definitions and statistical interpretation of the results. No significant excess of events above the SM prediction is observed in the signal regions. Therefore, the final result is interpreted by means of statistical tests designed to exclude regions of parameter space of specific SUSY models. For this thesis, the phenomenological Minimally Supersymmetric Standard Model (pMSSM) is tested, and exclusion limits are set on gaugino mass parameters (M_2 and mu). The exclusion regions are expanded since the previously published results based on the LHC 7 TeV collision data. By combining these results with those from searches with trilepton final states, the exclusion regions are further expanded, giving the strongest limits on the gaugino mass parameters to date.


Elementary Particles and High Energy




Carleton University

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