The Higgs as a portal to the hidden sector via an analysis of $H\to Zd_d Z_d \to 4l$ using the ATLAS detector

The Standard Model (SM) has well known deciencies, and there is clearly need for new physics beyond the SM. The particles manifesting the new physics would interact at most weakly with the SM particles, and hence they are termed dark. The Higgs boson is potentially a favourable route for the production of the dark particles. There are a large class of theories where couplings or mixings at the Higgs level leads to exotic Higgs decays, which nonetheless do not signicantly disturb the known physics below the Higgs level. This is therefore a signicant potential discovery opportunity. We present the motivation and progress made in the studies which have been carried out as part of designing the search for the exotic decay of the SM Higgs which proceeds via a dark force back to SM four leptons, H $\to$ Z$_d$Z$_d$ $\to$ 4l from the LHC run 1 data using the ATLAS detector.