Search For The Standard Model Higgs Boson In eτ Final States

Abstract

Presented in this dissertation is a search for the standard model (SM) Higgs boson using the DØ detector at Fermilab in Batavia, IL. The SM is a fantastically accurate theory describing the fundamental interactions and particles of the Universe. The only undiscovered particle in the SM is the Higgs boson, which is hypothesized to be responsible for electroweak symmetry breaking and giving mass to all other particles. Considered in this search is the process H + X -> eτhjj, where e is an electron, τh is the hadronic decay of a τ, and j is a jet, using pp̄ collisions at center of mass energy s⁻¹ = 1.96 TeV. This search includes three production modes: associated production, gluon fusion and vector boson fusion. It also utilizes two decay channels: H -> ττ and H -> WW. A new technique, dubbed the Global Boosted Decision Tree, is introduced which offers a means of providing continuity to a multivariate search as a function of a particular parameter, in this case, the mass of the Higgs boson. The observed (expected) limit on the ratio of cross section times branching fraction to the SM at 95% confidence level is 14.6 (16.0) at mH = 125 GeV. This result is combined with the related channel H + X -> μτhjj and produced an observed (expected) limit of 9.0 (11.3) at mH = 125 GeV.