Search for Invisible Higgs Bosons Produced via Vector Boson Fusion at the LHC Using ATLAS Detector

A variety of astrophysical observations showed direct evidence for the existence of dark matter which accounts for about 85% of matter in the universe and does not interact with ordinary matter, except through gravity. Despite its abundance, dark matter particles are very elusive and hard to spot and no experiment confirmed their existence. In this work the invisible Higgs sector was investigated where Higgs bosons are produced via the vector boson fusion (VBF) process and subsequently decay into invisible particles. The expectation for the branching fraction of invisible decays from the standard model is O(0.1)% but several scenarios beyond the standard model allow larger values of O(10)%. The hypothesis under consideration is that the Higgs boson might decay into a pair of weakly interacting massive particles (WIMPs) which are candidates to explain the existence of dark matter. The experimental signature in the detector is a pair of energetic jets and large missing energy. The analysis uses data samples of an integrated luminosity of 139 fb^-1of proton proton collisions at √s = 13 TeV recorded by ATLAS detector at the LHC. The observed number of events are found to be in agreement with the background expectation from standard model processes. Assuming a 125 GeV Higgs boson with a standard model production cross section, the observed and expected upper limits on the branching fraction of its decay into invisible particles are found to be 0.13 at 95% confidence level.