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

Abstract

A search for the neutral Higgs bosons predicted by the Minimal Supersymmetric Standard Model, <em>h, H</em> and <em>A</em>, is presented in this thesis. It is based on a data sample with an integrated luminosity of L_int = 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, <em>h/H/A</em> → τ_had τ_had. The selection of events is based on the kinematic and topological properties of a heavy neutral Higgs boson produced by <em> b<span style="text-decoration: overline">b</span></em> annihilation and the gluon-gluon fusion production mechanisms.<br /> The search significantly improves upon the sensitivity of previous searches, and leads the sensitivity of the <em>h/H/A</em> → ττ combined search, where other tau decay modes are selected in the final state, for signal masses m_A >∼ 350 GeV. <br /> As no significant excess is found, exclusion limits are set in the space of the two leading-order free parameters of the MSSM, <em>m_A</em> and tan<em>β</em>. After the discovery of a Higgs boson in 2012, with a mass of <em>m_H</em> = 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 <em>m_A</em> = 170 - 1000 GeV. Model-independent exclusion limits were also obtained for the cross-section of the production of a generic resonance, <em>φ</em>, by<em> b<span style="text-decoration: overline">b</span> </em>annihilation and gluon-gluon fusion. Excluded cross-sections at 95% confidence level are as high as σ_excl.(<em>b<span style="text-decoration: overline">b</span>→ φ → ττ</em>) ≈ 4.2 pb and σ_excl.(<em>gg →∅→ ττ</em>) ≈ 6.8 pb at <em>m_φ</em> = 170 GeV and <em>σ</em>_excl.(<em>b<span style="text-decoration: overline">b</span> → φ → ττ</em>) ≈ 9.2 fb and <em>σ</em>_excl.(<em>gg → φ → ττ</em>) ≈10 fb at <em>m_∅</em> = 1000 GeV.