Studies with Muons in ATLAS: TileCal Level-2 Trigger and MSSM Higgs Discovery Reach

This thesis was carried out in the years previous to the LHC start-up, i.e. during the ATLAS detector commissioning phase. It contains an introductory part about the detector and its expected physics performance and two main parts about the development of a Level-2 trigger for muons and a study of the MSSM Higgs discovery reach with simulated data, which are briefly described below. The first part of the thesis is devoted to TileMuId, the muon identication algorithm based on TileCal whose main goal is to be used as a Level-2 trigger of low-$p_{\text{T}}$ muons. A second version of TileMuId (ROD-based) has been implemented to run in the TileCal ROD DSPs. This involved developments in the DSP firmware and in the Athena framework, described in the document. In addition, studies of the algorithm performance in terms of efficiency and fraction of fakes have been done. Developments and studies to match the TileCal muon candidates with the Inner Detector tracks (provided by ID reconstruction algorithms) have been performed and two new trigger chains combining TileCal and ID have been created. Both TileMuId versions are fully integrated in the Muon Trigger Slice Working Group, have been running in High Level Trigger during cosmics data taking periods and are included in the trigger menu of ${\cal{L}}=10^{31}$ cm$^{-2}$s$^{-1}$. In the second part of the thesis, the ATLAS discovery potential of the MSSM neutral Higgs boson in the dimuon decay channel, $h/A/H \to \mu^{+}\mu^{-}$, for a center-of-mass energy of 14 TeV is explored with simulated data. For this analysis, we used the official event selection cuts agreed by the collaboration with the only exception of not requiring b-tagging for the jets. Since jet flavor tagging is not required in the analysis, it can be performed with low integrated luminosity, even before the b-tagging in the experiment reaches its optimal performance. Discovery significances and exclusion limits for several Higgs masses (110 GeV to 400 GeV) and $\tan\beta$ values (10 to 60) are evaluated using a maximum likelihood fit formalism based on toy Monte Carlo experiments at different integrated luminosities. Our results show that the MSSM parameter space can be significantly constrained with this analysis at 1 fb$^{-1}$ (a 95\% CL exclusion can be established for $m_A=130$ GeV and $\tan\beta>30$) and discovery is feasible at 10 fb$^{-1}$ ($5\sigma$ significance can be achieved for $m_A=130$ GeV and $\tan\beta>35$).