Search for an Invisibly Decaying Higgs Boson Produced via Vector Boson Fusion

This thesis presents the first search of an invisibly decaying Higgs boson produced via Vector Boson Fusion on ATLAS. The dataset used for the analysis corresponds to 20.3fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 8$ TeV recorded at the Large Hadron Collider in 2011 and 2012. An upper bound limit is set at 95% confidence level on the invisible branching fraction of the Higgs Boson. A limit of 28% is observed (34% expected) and interpreted using the Higgs portal model to set a limit on the dark matter-nucleon cross section. The unique jet final state created by Vector Boson Fusion provides a stronger signal to background ratio than other invisibly decaying Higgs channels. The Vector Boson Fusion analysis presented resulted in the strongest constraint on dark matter production set by a hadron collider.