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Search for the Standard Model Higgs Boson in Leptons Plus Jets Final States

Nguyen, Huong
Format
Thesis/Dissertation; Online
Author
Nguyen, Huong
Advisor
Hirosky, Robert
Abstract
We present searches for the production of a Standard Model Higgs boson (H) in the leptons plus jets final states with a data set corresponding to 9.7 fb−1 of integrated luminosity collected in proton-antiproton collisions at a center of mass energy of 1.96 TeV with the DØ detector at the Fermilab Tevatron Collider. The searches are carried out in two independent analyses accounting for different signal topologies. The ℓνjj analysis investigates events containing a charged lepton (electron or muon), a large missing transverse energy arising from the presence of a neutrino, and two or more jets. The search in this analysis is sensitive to associated production of the H with a W boson, WH->ℓνbb; gluon fusion with the Higgs boson decaying to a W boson pair, H->WW->ℓνjj; and associated production with a vector boson where the Higgs decays to a W boson pair, V H->VWW->ℓνjjjj (where V = W or Z). The ZH->ℓℓbb analysis performs a search for the Standard Model Higgs boson produced in association with a Z boson and subsequently decaying to a bottom and anti-bottom quark pair with a decay topology containing a pair of charged leptons and least two jets. We set upper limits at the 95% confidence level on the Standard Model Higgs boson production cross section in the mass range from 90 to 200 GeV for the ℓνjj analysis and in the mass range from 90 to 150 GeV for the ZH->ℓℓbb analysis. For a Higgs boson mass of 125 GeV, the observed (expected) limits for the ℓνjj and the ZH->ℓℓbb analyses are 7.1 (5.1) and 5.8 (4.7) times the standard model expectation, respectively. We also interpret the searches in the ℓνjj analysis in terms of models containing a fourth generation of fermions, as well as models with a fermiophobic Higgs boson. In these interpretations, we exclude the mass range 150-188 (190) GeV in the low-mass (high-mass) fourth generation fermion scenario, and provide upper limits at the 95% confidence level on the production cross section in the fermiophobic model. Each of ℓνjj and the ZH->ℓℓbb analyses provide inputs to the overall Tevatron combination of the Higgs boson searches. In the mass range 115-140 GeV, the data recorded at the Tevatron exhibit an excess above the background prediction of more than two standard deviations. At the Higgs boson mass of 125 GeV, where the largest contribution to the Higgs boson sensitivity at the Tevatron comes from the H->bb decay mode, we observe an excess in data consistent with the Higgs boson observed at the LHC, at the level of three standard deviations.
Language
English
Published
University of Virginia, Department of Physics, PHD (Doctor of Philosophy), 2014
Published Date
2014-01-30
Degree
PHD (Doctor of Philosophy)
Collection
Libra ETD Repository
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