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Searches for supersymmetric particles in events with two opposite-sign same-flavor leptons, jets, and large missing transverse energy

This thesis presents the search for Supersymmetric particles, in both strong and electroweak productions, in the same-flavor opposite-sign dilepton channel. The SUSY analyses usually require large missing transverse energy E T for the presence of invisible LSPs. One of the most difficult background processes to estimate in these searches is due to artificial etmiss from hadronic object (jet) energy mismeasurements, which are difficult to model in simulation due to the complexity of detector defects. One major focus of this thesis is to estimate such mismeasurements in the crucial background originating from SM production of Z boson in association with jets (Z + jets), where Z decays to two leptons. In addition to the jet mismeasurement, the artificial E T in Z + jets events also convolves the mismeasurement of lepton energy. A data-driven method is developed using photon data (γ + jets) events to model the jet mismeasurements in Z + jets events. To model the lepton resolution, I developed a data-driven deconvolution method, which deconvolves jet and lepton resolutions in a control region, to derive a resolution correction for the photons. The results of this thesis probe the gluino masses as large as ∼ 2 TeV, and gaugino masses as large as ∼ 600 GeV. However, the analyses are not yet sensitive to the parameter space of light electroweak gauginos. A new background method and a new analysis variable are also proposed in this thesis to improve the sensitivity to the light higgsinos, which are crucial for the SUSY solution to the hierarchy problem.