Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying to $W^\pm W^\mp$ or $ZZ$ in Fully Hadronic Final States Using $pp$ Collisions at $\sqrt s=13$~TeV Recorded with the ATLAS Detector

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. A pioneering search is performed for dark matter particles produced in association with a Dark Higgs boson $s$ decaying to $VV$ where $V=W^\pm,Z$, using 139~fb$^{-1}$ of $pp$ collisions recorded by the ATLAS detector at a center-of-mass energy of 13~TeV at the LHC. The $s\to V(q\bar q)V(q\bar q)$ decays are reconstructed with a novel technique using reclustered jets with a cone parameter $R=0.8$ based on $R=0.4$ calorimeter jets and tracking information. The observed data are found to agree with Standard Model predictions.