Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at $\sqrt{s}=13$ TeV

Current measurements permit the branching ratio of the SM Higgs to BSM particles to be as high as approximately 30%. Such exotic decays of the Higgs are well-motivated theoretically. Of particular interest is the decay of h to one or two dark sector particles called $Z_d$. This decay occurs in models where h interacts with a dark sector which could have a rich and interesting phenomenology like the SM. A dark sector could naturally address many of the questions left unanswered by the SM. A search is conducted for the 125 GeV Higgs decaying to one or two new BSM bosons that finally decay to four leptons ($l = e, \mu$). The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 36.1 fb$^{-1}$. Improvements to the search using the full 2015-8 data-set are also presented.