Charged Higgs boson searches and SemiConductor Tracker commissioning for the ATLAS experiment

The ATLAS (A Toroidal Lhc ApparatuS) experiment is one of four major experiments presently being installed at the upcoming Large Hadron Collider (LHC) at the European Centre for Nuclear Research (CERN) outside Geneva. In this thesis we present work done on both the simulation of the ATLAS physics potential for a charged Higgs boson and the construction of the Semiconductor Tracker (SCT) - a subdetector within the ATLAS Inner Detector. The discovery of a charged Higgs boson would be an unambiguous sign of physics beyond the Standard Model (SM) and it is thus of great interest to study the ATLAS potential for a charged Higgs discovery. Two such studies have been conducted for this thesis. In the first study a large-mass-splitting Minimal Supersymmetric Standard Model (MSSM) is assumed in which the charged Higgs boson decays into a W boson and a neutral Higgs may receive a large branching ratio.We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large irreducible SM background. Despite its small brancing ratio at high masses for the charged Higgs boson, the decay mode H± →τν remains the most powerful decay mode for a charged Higgs discovery. Discovery through this channel depends heavily on excellent detector performance and understanding of the background.We show that with detector full simulation and with more complete background samples this channel still remains the most powerful decay mode. We also show that it is possible to connect the discovery countour for charged Higgs boson masses below and above the top-quark mass. The SCT detector is a tracking detector based on silicon microstrip detector technology. It is a highly modular detector consisting of 4088 detector modules that are mounted on 4 barrels and 9x2 end cap disks. Some 320 of the SCT barrel detector modules were built by a Scandinavian collaboration and presented here are the results of this work and procedures for building and quality assurance. Each SCT detector module is powered by an individual high and low voltage supply and thus a large scale and robust power supply control system is needed for controlling the SCT detector. Presented in this thesis is work done to prepare the SCT power supply software for this task, as well as the results obtained during testing and development. As a part of the commissioning of the completed SCT barrel, a series of cosmic runs were performed. Data from these runs allowed for first studies of the detector alignment and alignment results and conlusions thereof are presented in this thesis.