Search for single-production of vector-like quarks decaying into $\textit{Wb}$ in the fully hadronic final state in $\textit{pp}$ collisions at = 13 TeV with the ATLAS detector

A search for $\textit{T}$ and $\textit{Y}$ vector-like quarks produced in proton-proton collisions at a centre-of-mass energy of 13 TeV and decaying into $\textit{Wb}$ in the fully hadronic final state is presented. The search uses 139 fb of data collected by the ATLAS detector at the LHC from 2015 to 2018. The final state is characterised by a hadronically decaying $\textit{W}$ boson with large Lorentz boost and a $\textit{b}$-tagged jet, which are used to reconstruct the invariant mass of the vector-like quark candidate. The main background is QCD multijet production, which is estimated using a data-driven method. Upon finding no significant excess in data, mass limits at 95% confidence level are obtained as a function of the global coupling parameter, $\textit{κ}$. The observed lower limits on the masses of $\textit{Y}$ quarks with $\textit{κ}$ = 0$\textit{.}$5 and $\textit{κ}$ = 0$\textit{.}$7 are 2$\textit{.}$0 TeV and 2$\textit{.}$4 TeV, respectively. For $\textit{T}$ quarks, the observed mass limits are 1$\textit{.}$4 TeV for $\textit{κ}$ = 0$\textit{.}$5 and 1$\textit{.}$9 TeV for $\textit{κ}$ = 0$\textit{.}$7.