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Title:A search for the Higgs boson in H->WW->lvlv with 8.2 fb-1
Author(s):Carls, Benjamin
Director of Research:Pitts, Kevin T.
Doctoral Committee Chair(s):Neubauer, Mark S.
Doctoral Committee Member(s):Pitts, Kevin T.; Thaler, Jonathan J.; Willenbrock, Scott S.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Collider Detector at Fermilab (CDF)
Abstract:This thesis documents a search for Standard Model (SM) Higgs boson to WW production in the final state of two charged leptons (e, μ) and two neutrino final state resulting from in pp collisions at √ s = 1.96 TeV. The data collected by the CDF II detector at the Tevatron collider at Fermilab, corresponds to an integrated luminosity of 8.2 fb−1. This iteration of the analysis incorporated several improvements to increase Higgs sensitivity. We reevaluated lepton isolation values to recover signal events in which leptons mutually spoil each other’s isolation requirements. We additionally incorporated new lepton identification selections, namely likelihood based forward electrons and a better recovery of electrons passing through detector cracks. The base analysis searches for opposite-sign dilepton events. We employed three separately trained neural networks to distinguish signal from background processes for events with 0, one, or two jets. To further increase sensitivity for 0-jet events, we constructed a likelihood ratio discriminant based on Matrix Element calculations as an additional input to the neural network. For the base opposite-sign analysis, summing over all jet multiplicities, we observed 3513 events in data compared with a background expectation of 3409 ± 233 and a signal expectation of 53.6 ± 9.4 for a mass of 165 GeV/c2. To further increase signal acceptance, we incorporated several separate search regions in addition to the base analysis. We include subchannels searching for Higgs production in events with low dilepton invariant mass and in events having final states with either same-sign dileptons or trileptons With the combination of the separate analyses, we observed a 95% C.L. upper production limit of 0.77 times the SM expectation for a Higgs mass of 165 GeV/c2 to be compared with the value for the median of the expected limit (0.78). We additionally present results for eighteen Higgs masses ranging from 110 GeV/c2 to 200 GeV/c2. We excluded at the 95% C.L., a SM Higgs boson in the mass range between 156 and 175 GeV/c2.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Benjamin Carls
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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