Search for High-Mass Resonant Top-Antitop Pair Production in Lepton+Jets Events in 8 TeV pp Collisions
thesisposted on 21.07.2015, 00:00 by Paul J. Turner
A model-independent search for high-mass resonant top-antitop quark pair production in 8 TeV center-of-mass energy proton-proton collisions recorded by the Compact Muon Solenoid experiment at the Large Hadron Collider in 2012 is presented. Data samples corresponding to 19.7 inverse femtobarns of integrated luminosity were analyzed and compared to Standard Model predictions. Events consistent with the semileptonic decay of a boosted top-antitop quark pair, containing exactly one muon or electron and at least two high transverse momentum jets, were selected for analysis. Jet substructure analysis was employed to tag events containing boosted hadronic top quark decays, enabling the sensitivity of the search to be improved significantly compared to previously published analyses using the same dataset. The invariant mass of the top-antitop quark pair is reconstructed using a chi-squared approach, and is used to look for evidence of massive new resonances above the Standard Model predictions. With no evidence of significant deviations from the Standard Model predictions, we use a Bayesian statistical model to set 95% Confidence Level limits on the production cross-section time branching ratio for 1% and 10% width resonances. In addition, we set model-specific limits at 95% Confidence Level for two benchmark models that predict resonant top-antitop quark pair production: Topcolor Z' bosons and Kaluza-Klein excitations of gluons in Randall-Sundrum models. We then present a combined result, in which parallel analyses searching for resonant top-antitop quark pairs that decay fully leptonically or all hadronically are combined with this analysis, that represents the strongest limits on resonant top-antitop quark pair production to date.