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Searches for invisibly decaying Higgs bosons using the Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) and their interpretations are described. These searches are motivated both by a desire to characterise the newly observed Higgs boson, and by the cosmological observation of very weakly interacting matter in the universe, which is called dark matter. In order to provide context for these searches, introductions to the Standard Model (SM) of particle physics and several extensions to the SM which incorporate dark matter are given. The searches described in this thesis use data recorded in proton-proton collisions in 2012 and focus on the most sensitive mode, Vector Boson Fusion (VBF) production. The first search uses 19.5 fb 1 of data promptly reconstructed in 2012 and results in an observed (expected) limit on the invisible branching fraction of the 125 GeV Higgs boson, B (H -> inv), of 0.65 (0.49) at the 95% confidence level (CL) [1]. The second search uses 19.2 fb 1 of data collected using triggers with looser thresholds and reconstructed later, in 2013. This search resulted in an observed (expected) limit on B (H -> inv) of 0.57 (0.40) at the 95% CL [2]. Combinations of these searches with searches in other production channels are also described, the most sensitive of which results in an observed (expected) limit on B (H -> inv) of 0.36 (0.30) at 95% CL [3]. Projections of the sensitivity of these analyses in Run 2 and interpretations of their results as limits on various models of dark matter are also given [4]. |
