Identification of Hadronically Decaying Tau Leptons in Searches for Heavy MSSM Higgs Bosons with the CMS Detector at the CERN LHC

This thesis describes methods for the reliable identification of hadronically decaying $\tau$ leptons in the search for heavy Higgs bosons of the minimal supersymmetric standard model of particle physics (MSSM). The identification of the hadronic $\tau$ lepton decays, i.e. $\tau$-jets, is applied to the $gg -> b\bar{b}H(A) -> \tau\tau$ and $gg \to tb H^{+-} -> \tau^{+-}\nu^{\tau}$ processes to be searched for in the CMS experiment at the CERN Large Hadron Collider. Of all the event selections applied in these final states, the $\tau$-jet identification is the single most important event selection criterion to separate the tiny Higgs boson signal from a large number of background events. The $\tau$-jet identification is studied with methods based on a signature of a low charged track multiplicity, the containment of the decay products within a narrow cone, an isolated electromagnetic energy deposition, a non-zero _$\tau$lepton flight path, the absence of electrons, muons, and neutral hadrons in the decay signature, and a relatively small $\tau$ lepton mass compared to the mass of most hadrons. Furthermore, in the $H^{+-} -> \tau^{+-}\nu_{\tau}$ channel, helicity correlations are exploited to separate the signal $\tau$ jets from those originating from the $H^{+-} -> \tau^{+-}\nu_{\tau}$ decays. Since many of these identification methods rely on the recons truction of charged particle tracks, the systematic uncertainties resulting from the mechanical tolerances of the tracking sensor positions are estimated with care. The $\tau$-jet identification and other standard selection methods are applied to the search for the heavy neutral and charged Higgs bosons in the $H,A -> \tau^{+-}\nu_{\tau}$ decay channels. For the $H^{+-} -> \tau^{+-}\nu_{\tau}$ channel, the _$\tau$-jet identification is redone and optimized with a recent and more detailed event simulation than previously in the CMS experiment. Both decay channels are found to be very promising for the discovery of the heavy MSSM Higgs bosons. The Higgs boson(s), whose existence has not yet been experimentally verified, are a part of the standard model and its most popular extensions. They are a manifestation of a mechanism which breaks the electroweak symmetry and generates masses for particles. Since the $H,A -> \tau\tau$ and $H^{+-} -> \tau^{+-}\nu_{\tau}$ decay channels are important for the discovery of the Higgs bosons in a large region of the permitted parameter space, the analysis described in this thesis serves as a probe for finding out properties of the microcosm of particles and their interactions in the energy scales beyond the standard model of particle physics.