A search for a charged Higgs boson in the H+ → tb channel and tagging of b jets with the Atlas experiment at the LHC

The only particle of the Standard Model that has not yet been discovered is the Higgs boson, which explains the origin of the masses of elementary particles. In the Minimal Supersymmetric extension to the Standard Model (MSSM), the Higgs sector consists of five bosons, two of which are charged. The search for a charged Higgs boson in the gg → t-bar bH+(H+ → tb-bar) channel, is the main topic of this analysis. We present an analysis that uses a likelihood function to resolve combinatorial possibilities while reconstructing the charged Higgs boson, and the b-tagging to suppress the tt-bar + jets background. We also present the difficulties due to the combinatorial background reducing the discovery potential of this channel. The presence of 4 b quarks in the final state that we are looking for, makes the b-tagging an important tool for the analysis. Therefore, a part of this work is dedicated to the study of b-tagging. We present in the context of the preparation for the first data, several studies dedicated to the optimisation and the understanding of the b-tagging performance. We also present the commissioning of a simple tagger (JetProb) to be used with first data analysis. (author)