Search for $W' \rightarrow tb \rightarrow qqbb$ decays in $pp$ collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector

A search for a massive $W'$ gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in $pp$ collisions at the LHC. The dataset was taken at a centre-of-mass energy of $\sqrt{s} = 8{\mathrm {\ TeV}}$ and corresponds to $20.3\,\text{ fb }^{-1}$ of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass $W'$ bosons in the range 1.5–3.0  ${\mathrm {\ TeV}}$ . $b$ -tagging is used to identify jets originating from $b$ -quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the $W'\rightarrow tb$ cross section times branching ratio ranging from $0.16\,\mathrm {pb}$ to $0.33\,\mathrm {pb}$ for left-handed $W'$ bosons, and ranging from $0.10\,\mathrm {pb}$ to $0.21\,\mathrm {pb}$ for $W'$ bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the $W'$ -boson coupling to $tb$ as a function of the $W'$ mass using an effective field theory approach, which is independent of details of particular models predicting a $W'$ boson.