Search for dark matter particles produced in association with a dark Higgs boson decaying into $W^{+}W^{-}$ in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ with the CMS detector

A search for dark matter (DM) particles is performed using events with a pair of W bosons and large missing transverse momentum. The analysis is based on proton-proton collision data at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC between 2016 and 2018 corresponding to an integrated luminosity of $137~\mathrm{fb}^{-1}$. No significant excess in the $W^{+}W^{-}$ dileptonic decay channel over the expected standard model background is observed. Limits are set on DM production in the context of the dark Higgs simplified model, with a dark Higgs mass above the $W^{+}W^{-}$ pair mass threshold.