Search for Supersymmetry with Hadronically and Leptonically Decaying Tau Leptons at the ATLAS Experiment

Abstract

The search for physics beyond the Standard Model (SM) is a central focus of modern particle physics. Supersymmetric extensions (SUSY) to the SM offer elegant solutions to many unresolved questions of the theory. This thesis presents the results of a search for SUSY at the LHC that was performed using a dataset of 8 TeV proton-proton collisions with 20.3 fb-1 integrated luminosity recorded by the ATLAS detector in 2012. The SUSY models considered for this thesis feature decays of SUSY particles that include multiple tau leptons in the final state. The signature is further defined by one additional light lepton, highly energetic jets and large missing transverse momentum. Eight optimized signal regions are defined to investigate four different SUSY models. The contributions from SM background in these signal regions are estimated using Monte Carlo simulation. From SM control regions scaling factors to normalize the MC event counts are obtained. No significant excess is observed in any of the signal regions. This result is interpreted in form of exclusion limits in the parameter space of the considered SUSY scenarios. Furthermore, a model-independent limit is derived for each signal region. The exclusion at 95% confidence level reaches in the GMSB model up to Λ ≈ 70 TeV, corresponding to a gluino mass of 1.5 TeV. For the nGM model the parameter space below gluino masses of 1 TeV can be excluded. The interpretation in the bRPV model excludes parts of the parameter space up to m0 ≈ 1 TeV. For mSugra the limit reaches up to m1/2 ≈ 500 GeV for low m0. A statistical combination with other SUSY searches using tau final states further improves the strength of the exclusion limits.