Search for the Standard Model Higgs boson produced with an associated W boson and decaying to a pair of $b$ quarks at $\sqrt{s} = 13$ TeV with the ATLAS detector

A Higgs boson has been found in multiple decay modes, but not yet in the mode with the largest standard model (SM) branching fraction: $H \rightarrow b\bar{b}$. This thesis details a search for the SM Higgs when produced with an associated $W$ boson. This search is performed with the ATLAS detector using data from Run 2 of the Large Hadron Collider operating at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 36.1 $fb^{-1}$. The final state of the $W$ boson is its leptonic decay with an electron or muon. The measured signal strength relative to the SM Higgs prediction is μ = 1.35$^{+0.40}_{-0.39}$(stat.)$^{+0.56}_{-0.47}$(syst.) and the probability that observed data arises from a background fluctuation only gives a gaussian equivalent of 2.30 standard deviations compared to the expected value of 1.80 standard deviations. Combined with additional leptonic modes of associated vector boson production with a $Z$ boson, the significance of $H \rightarrow b \bar{b}$ is observed at 3.5 standard deviations compared to an expected 3.0 standard deviations with a signal strength of μ = 1.20$^{+0.24}_{-0.23}$(stat.)$^{+0.34}_{-0.28}$(syst.) The combined search demonstrates evidence for both the Higgs boson’s decay to $b$-quarks and for its production in association with a vector boson.