Search for vector boson resonances decaying to a top quark and a bottom quark in the hadronic final state using $pp$ collisions at $\sqrt{s}~=~13$ TeV with the ATLAS detector

A search for a new charged massive gauge boson, $W'$, is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}~=~13$~TeV, and corresponds to an integrated luminosity of 139~fb$^{-1}$. The invariant mass of the $W'$ boson is reconstructed in the decay mode $W' \rightarrow tb$ with hadronic decay of the top quark. The result is interpreted in terms of a leptophobic $W'$ boson with right-handed chirality in a mass range of 1.5-5~TeV, with the same coupling strengths to the quarks as the Standard Model $W$~boson. No significant deviation from the background prediction is observed, and the results are expressed as upper limits on the $W' \rightarrow tb$ production cross-section times branching ratio as a function of the $W'$-boson mass. These limits exclude a $W'$ boson with right-handed couplings with mass below 4.4~TeV at the 95% confidence level.