  Despite dark matter abundance, its nature remains elusive. Many searches of
dark matter particles are carried out using different technologies either via
direct detection, indirect detection, or collider searches. 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 hypothesis under consideration is that the Higgs boson might
decay into a pair of weakly interacting massive particles (WIMPs), which are
candidates for dark matter. The observed number of events are found to be in
agreement with the background expectation from Standard Model (SM). Assuming a
125 GeV Higgs boson with SM 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. Combination of searches for an
invisibly decaying Higgs boson produced via the main Higgs production modes at
the LHC using 2011-2018 data is conducted and discussed.
