Optimization of CMS Detector Performance and Detection of the Standard Model Higgs Boson via the $qqH, H \to \tau\tau$ Channel with a Lepton + a Jet in the Final State

The Compact Muon Solenoid (CMS) is a general purpose detector at the Large Hadron Collider (LHC) designed to enable physics studies in the multi-TeV energy range. This thesis contains simulation studies on the performance of two of the CMS sub-detectors, the Silicon Strip Tracker and the Electromagnetic Calorimeter (ECAL), and results from a study which investigated the potential of observing the Standard Model Higgs boson via the qqH, H -> tautau channel with a lepton and a jet in the final state. New algorithms have been developed to measure and monitor the pedestals of the Silicon Tracker during data taking, and to improve the online calculation of the common mode offset. The variation of the fraction of energy contained in reconstructed clusters of fixed size over the true energy for single photon and electron events in the barrel ECAL has been studied. Due to the ECAL geometry, the fractional energy varies by 0.7% in the pseudorapidity range between the centre (eta= 0) and the forward end (eta= 1.479) of the barrel. This originates primarily from front leakage of the shower. An algorithm for reconstructing the mass of the eta meson from high ET eta events has been developed for intercalibrating the ECAL crystals at the start of the LHC operation. Simulation studies demonstrate that the algorithm achieves a reconstructed eta mass resolution of 4.6%. The H -> tautau decay channel is promising for the discovery of a Higgs boson with mass below 150 GeV/c^2 if production via the vector boson fusion (VBF) process is considered. Studies of background rejection methods based on the characteristics of the VBF process have been performed for the first time using fully simulated signal and background events. These studies have demonstrated that about 10 Higgs boson decay events are expected to be observed with a statistical significance of 3.8 sigma (mass = 135 GeV/c^2) using an integrated luminosity of 30 fb^-1. It is expected that this luminosity can be achieved within the first three years of LHC operation.