ATLAS Searches for Higgs Boson Decays to BSM Dark-Z Bosons in Four-Lepton Final States

ATLAS searches for a BSM light boson using as portal events where a Higgs boson with mass 125 GeV decays to four leptons are reported. This decay is presumed to occur via an intermediate state which contains one or two on-shell, promptly decaying bosons: H → ZX/XX → 4l, where X is a new dark vector boson $Ζ_d$ (or a pseudo-scalar a), with mass between 1 and 60 GeV. These exotic Higgs decays searches are using Run-2 139 fb$^{-1}$ data from p-p collisions at $\sqrt{s}$=13 TeV collected with the ATLAS detector at the LHC. The results are found to be consistent with SM background predictions and limits are set with interpretations in specific benchmark theory models.