Search for $\mathrm{W}\gamma$ resonances using hadronic decays of Lorentz-boosted $\mathrm{W}$ bosons in proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$

A search for $\mathrm{W}\gamma$ resonances in the mass range between 700 and 6000 $\mathrm{GeV}$ is presented. The $\mathrm{W}$ boson is reconstructed via its hadronic decay, with the final-state products forming a single, large-radius jet, owing to a large Lorentz boost of the $\mathrm{W}$ boson. The search is based on proton-proton collision data at $\sqrt{s} = 13~\mathrm{TeV}$, collected with the CMS detector in 2016--2018, corresponding to an integrated luminosity of $137~\mathrm{fb}^{-1}$. The $\mathrm{W}\gamma$ invariant mass spectrum is parameterized with a smoothly falling background function and examined for the presence of resonance-like signals. No significant excesses above the predicted background are observed. Model-specific limits at $95\%$ confidence level on the production cross section times branching fraction to the $\mathrm{W}\gamma$ channel are set for narrow resonances and for resonances with an intrinsic width equal to $5\%$ of their mass, for spin-0 and spin-1 hypotheses, ranging between 0.11 and 35 fb. These are the most restrictive limits to date on the existence of such resonances. Model-independent limits on the production cross section times branching fraction to the $\mathrm{W}\gamma$ channel times signal acceptance are also set for minimum $\mathrm{W}\gamma$ mass thresholds between 1500 and 8000 $\mathrm{GeV}$, allowing for testing more general models predicting production of a photon in association with a jet consistent with a hadronic $\mathrm{W}$ or $\mathrm{Z}$ boson decay.