Search for Higgs Decays to Beyond the Standard Model Light Gauge Bosons in four-lepton events with the ATLAS Detector at √s = 13 TeV

Hidden sector or dark sector states appear in many extensions to the Standard Model, to provide a candidate for the dark matter in the Universe or to explain astrophysical observations of positron excesses. A hidden or dark sector can be introduced with an additional U(1)d dark gauge symmetry. We present model-independent searches for dark sector states and interpret the results in benchmark models where the dark gauge symmetry is mediated by a dark vector boson Zd promptly decaying into pairs of same-sign opposite-flavour leptons. The results reported here use the pp collision data sample collected in 2015 and 2016 by the ATLAS detector at the LHC with a centre-of-mass energy of 13 TeV.