Search for charged Higgs bosons decaying via $H^\pm \rightarrow \tau^\pm\nu$ in fully hadronic final states with the ATLAS detector at the LHC

Searches for charged Higgs bosons decaying to a tau lepton and a neutrino in fully hadronic final states are presented in this thesis. The analyses are based on 4.6fb$^{-1}$ and 19.5fb$^{-1}$ of proton-proton collision data taken with the ATLAS detector at the LHC at center-of-mass energies of 7TeV and 8TeV in 2011 and 2012, respectively. Charged Higgs bosons with masses less than the top quark mass are searched for in events consistent with top-quark pair production and charged Higgs bosons with masses greater than the top quark mass are searched for in associated production with a top quark. In the search based on data taken in 2011, all background contributions are estimated in data-driven ways. Only a minor background contribution is estimated using simulation in the searches based on data taken in 2012; all dominant background contributions are estimated using data-driven methods here as well. An embedding method is used in all searches to assess the dominant and irreducible background contributions containing true hadronically decaying tau leptons and described in detail in this thesis. No significant excess of the data compared to the background expectations due to Standard Model processes is observed. Statistical analyses lead to 95% confidence-level upper limits on the branching ratios $B(t\rightarrow bH^\pm)\times B(H^\pm\rightarrow\tau^\pm\nu)$ between 0.23% and 1.3% for charged Higgs boson masses between 80GeV and 160GeV and on the production cross section times branching ratio, $\sigma(pp\rightarrow tH^\pm+X)\times B(H^\pm\rightarrow\tau^\pm \nu)$ ranging from 0.76pb to 4.5fb for charged Higgs boson masses between 180GeV and 1000GeV. The branching ratio and cross section limits are used to derive constraints on the parameter space of minimal supersymmetric extensions of the Standard Model in various benchmark scenarios. These limits are the so far strictest limits set by the ATLAS collaboration in the search for charged Higgs bosons in fully hadronic final states.