Studies of Charged Higgs Boson Observability in the $H \to tb$ Decay at the ATLAS Experiment within the Minimal Supersymmetric Standard Model

This thesis presents a Monte Carlo study of the search for charged Higgs bosons heavier than the mass of the top quark within the Minimal Supersymmetric Standard Model (MSSM) at the ATLAS experiment at the CERN Large Hadron Collider. Charged Higgs bosons are predicted in many non-minimal Higgs extensions of the Standard Model. Their discovery would be a clear signal for the existence of New Physics beyond the Standard Model, possibly the first experimental evidence to be found if the MSSM is realized in nature. The feasibility of detecting the heavy charged Higgs boson with a mass up to 600 GeV is studied in the decay channel $H^{+}\rightarrow \bar{t}b$ for an integrated luminosity of 30 $fb^{−1}$ at a center-of-mass energy of $\sqrt{s}$=10TeV. A major difficulty for charged Higgs boson reconstruction is the combinatorial background in the complex multi-jet final state environment. It is shown that this can be overcome by applying a kinematic fitting procedure and by a subsequent cut-based event and candidate selection. An iterative solution of the developed kinematic fit with non-linear constraints is presented. In addition, the reconstruction of charged Higgs bosons makes high demands on the ability to identify jets containing b-hadrons. A special b-tagging algorithm is introduced and a comparison with first ATLAS data is presented showing good agreement of the expected performance. This study is performed with a realistic simul ation of the ATLAS detector and takes into account all dominant experimental uncertainties and statistical uncertainties arising from limited Monte Carlo statistics. The result is given in terms of discovery and exclusion contours in the $(m_{H^{+}}, tan\beta)$ parameter space in the $m_{h}$-max scenario of the MSSM. This study indicates that the heavy charged Higgs boson can be discovered in this decay channel only for large values of $tan\beta$. It, however, can contribute to a combined $H^{+}$ sensitivity including other decay channels. Compared to previous studies the discovery reach could be improved.