Download or read book Identification of $\tau$ Leptons and Higgs Boson Search in the $\mu+\tau$ Final State at the D0 Experiment at the Tevatron written by and published by . This book was released on 2011 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: The gauge symmetry is the heart of our understanding of the electroweak interaction and describes all the current experimental results. However, the intrinsic incompatibility between the gauge invariance and the mass of particles leads to the introduction of a new particle, the Higgs boson, for which we have no experimental evidence as of today. This thesis describes the Higgs boson search in the [mu] + [tau] final state in 7.3 fb-1 of pp collisions at √s = 1.96 TeV collected by the DØ detector at the Tevatron. This analysis completes the golden channels (dimuons, electron-muon, dielectrons) exploiting the decay chain H → WW → lvlv , which is the main Higgs boson decay mode in the mass window accessible to the Tevatron. Since the final state includes a lepton, work was done to improve their identification among jets. An increase of 15% was achieved thanks to the the following : changing tuning parameters for the identification neural network, use of the kinematical dependence of the algorithm performances, incorporation of the [tau] lepton life time information and full study of the additionnal information coming from the central preshower measurements. Then, since the dominant background of the [mu] + [tau] Higgs boson search is W+jets (where one jet fakes a [tau] ), a method was developed to obtain good modeling of this background, not provided by the default simulation. This method is based, among other things, on the charge correlation between the muon and the [tau] candidate which allows for calibration of this background in the data excluding the signal region. Finally, all the kinematic and/or topological differences between the signal and the background were exploited to optimize this search, reaching an (observed) expected sensitivity of 7.8 (6.6) times the Standard Model for mH = 165 GeV=c2. In addition, this result was also interpreted in a fourth fermion generation scenario. For the first time, this analysis is included in the D and Tevatron combinations, both presented at Moriond EW and EPS 2011.