Search for dark Higgsstrahlung in e+e− → μ+μ− and missing energy events with the KLOE experiment

We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U   and a dark Higgs boson h′h′, with the KLOE detector at DAΦNE. We investigated the case of h′h′ lighter than U, with U   decaying into a muon pair and h′h′ producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2mμ