Search for Neutral Higgs Bosons of the MSSM decaying to τhad τhad in proton-proton collisions at √s = 8 TeV with the ATLAS detector

A search for the neutral Higgs bosons predicted by the Minimal Supersymmetric Standard Model, h, H and A, is presented in this thesis. It is based on a data sample with an integrated luminosity of Lint = 19.5 fb−1 from proton-proton collisions with a center-of-mass energy of √ s = 8 TeV produced at the LHC and recorded by the ATLAS experiment in 2012. The search is performed in the decay channel with two tau leptons decaying hadronically, h/H/A → τhadτhad. The selection of events is based on the kinematic and topological properties of a heavy neutral Higgs boson produced by bb¯ annihilation and the gluon-gluon fusion production mechanisms. The search significantly improves upon the sensitivity of previous searches, and leads the sensitivity of the h/H/A → ττ combined search, where other tau decay modes are selected in the final state, for signal masses mA & 350 GeV. As no significant excess is found, exclusion limits are set in the space of the two leading-order free parameters of the MSSM, mA and tanβ. After the discovery of a Higgs boson in 2012, with a mass of mH = 125.09 ± 0.24 GeV, new phenomenological scenarios of the MSSM were proposed. In this search, exclusion limits are obtained for these various scenarios in the mass range mA = 170 − 1000 GeV. Model-independent exclusion limits were also obtained for the cross-section of the production of a generic resonance, φ, by bb¯ annihilation and gluon-gluon fusion. Excluded cross-sections at 95% confidence level are as high as σexcl.(bb¯ → φ → ττ) ≈ 4.2 pb and σexcl.(gg → φ → ττ) ≈ 6.8 pb at mφ = 170 GeV and σexcl.(bb¯ → φ → ττ) ≈ 9.2 fb and σexcl.(gg → φ → ττ) ≈ 10 fb at mφ = 1000 GeV.