Top-Quark and Charged Higgs Boson Production at Hadron Colliders : Data Analysis at the DØ Experiment and Simulations for the ATLAS Detector

• Main Author: Gollub, Nils
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för kärn- och partikelfysik 2005
• Subjects: Elementary particle physics; ATLAS; LHC; charged Higgs boson; MSSM; D0; Tevatron; top quark; elementary particle physics; Elementarpartikelfysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6174; http://nbn-resolving.de/urn:isbn:91-554-6413-0

This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers. Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics. If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found. If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM. In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background. Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.