Search for diboson resonance production in the $\ell\nu qq$ final state using $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector at the LHC

A search is presented for new resonances decaying to $WW$ or $WZ$ final states, where one $W$ boson decays leptonically (to an electron or a muon plus a neutrino) and the other $W/Z$ boson decays hadronically. The data analyzed comprises 13.2 $\rm{fb}^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV, recorded by the ATLAS detector at the CERN Large Hadron Collider. The results are interpreted in the context of a spin-2 Randall-Sundrum bulk graviton, a new heavy vector boson, or an additional Higgs boson in the narrow width approximation. No evidence for resonant diboson production is observed. Resonance masses below 1240 GeV are excluded at 95% confidence level for a spin-2 Randall-Sundrum bulk graviton. The results also exclude a possible new neutral (charged) heavy vector boson coupling to the Higgs and the SM gauge bosons with masses below 2500 - 2810 (2400 - 2540) GeV, depending on the model, at 95% confidence level.