Elliot D. LipelesVanguri, Rami Sesha2023-05-222015-07-232016-11-292015-01-012016-11-29https://repository.upenn.edu/handle/20.500.14332/28953This 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.188 p.application/pdfRami Sesha VanguriPhysicsDissertation/Thesis