Physics Colloquium

The discovery of a Higgs boson at the LHC opens new research areas for instance the search for beyond-the-Standard-Model physics in the decays of the discovered Higgs boson. In events with large missing energy associated with jets, we search for the vector boson fusion production of the Higgs boson with forward jets, and the Higgs boson decays to invisible particles that result in large missing energy in the detector. An interpretation is done for the search for dark matter as a weakly interacting massive particle (WIMP) in the Higgs boson decays. We further carry out a statistical combination with other searches of Higgs boson decays to invisible particles to improve sensitivity. The current ATLAS exclusion limit combining all these searches is the best limit so far at the LHC on the invisible decay of the Higgs boson and the Higgs portal dark matter. In data events with four leptons in the final state, consistent with the decay of the Higgs boson to four leptons, we search for light-beyond-the-Standard-Model gauge boson Zdark that decay to a pair of same flavor and opposite sign leptons (electrons or muons): H -> Z(Zdark) Zdark -> 4l. The light gauge boson Zdark is predicted in extensions to the Standard Model to explain the muon g-2 anomaly and provide a candidate for dark matter.