Search for the Standard Model Higgs boson in the H --> WW --> lvqq channel

One of the biggest recent successes of the standard model (SM) was the 2012 discovery of a new scalar particle consistent with an SM-like Higgs boson by the CMS and ATLAS experiments at the Large Hadron Collider (LHC). The production of Higgs particles and their subsequent decay allows many distinct final states to be observed. Presented here is a search for an SM Higgs boson with mass $\simeq$125 GeV that decays through two W bosons, where one W decays hadronically and the other leptonically. While H --> WW has been observed at the LHC in the fully-leptonic final state, analyses in the lvqq channel have not yet achieved sufficient sensitivity to a low-mass Higgs. This analysis was optimized directly for a low-mass Higgs boson and aims to complement the observations of the Higgs in this regime. The decay chain H --> WW --> lvqq requires one W boson to have an off-shell mass; further, the presence of a neutrino in the final state makes Higgs mass reconstruction difficult. Finally, this decay channel suffers from a large irreducible background from W+jets production. This dissertation presents a search for the semi-leptonic W decay via a multivariate analysis of the 2012 8 TeV proton-proton collision data, a total luminosity of ~19/fb, collected at CMS.