A search for neutral high-mass Higgs bosons decaying into pairs of hadronically decaying tau leptons in 13 TeV collisions recorded by the ATLAS detector

This thesis outlines the search for neutral Higgs bosons in a mass range of $m_{H/A} = 200\,\mathrm{GeV} - 1.2\,\mathrm{TeV}$, decaying to a pair of hadronically decaying tau leptons. The search is performed using $\sqrt{s} = 13\,\mathrm{TeV}$ proton-proton collision data, corresponding to an integrated luminosity of $3.21\,\mathrm{fb^{-1}}$, recorded by the ATLAS detector. No excess over the predicted Standard Model background is observed and upper limits are placed on the production cross section times branching fraction as a function of the mass of the scalar resonance. When combined with the results of the analysis where one of the tau leptons decays to either a muon or electron, the 95 % confidence level upper limit on the cross section times branching fraction ranges from 1.4 pb at $m_{H/A} = 200\,\mathrm{GeV}$ to 0.025 pb at $m_{H/A} = 1.2\,\mathrm{TeV}$ for a scalar boson produced via gluon-gluon fusion, and 1.6 pb at $m_{H/A} = 200\,\mathrm{GeV}$ to 0.028 pb at $m_{H/A} = 1.2\,\mathrm{TeV}$ for a scalar boson produced via $b$-associated production. The results are interpreted in the Minimal Supersymmetric extension to the Standard Model (MSSM) as a limit on the value of $\,\mathrm{\tan}\beta$, as a function of the mass of the neutral CP-odd MSSM Higgs boson. In the $m_h^{\,\mathrm{mod+}}$ scenario, the 95 % confidence level upper limit is $\,\mathrm{\tan}\beta < 7.6$ for $m_{A} = 200\,\mathrm{GeV}$, and $\,\mathrm{\tan}\beta < 47$ for $m_{A} = 1\,\mathrm{TeV}$. For the mass range $m_{A} > 500\,\mathrm{GeV}$, the upper limit on $\,\mathrm{\tan}\beta$ is improved in comparison to previous ATLAS searches.