Search for single-production of vector-like quarks decaying into <i>Wb</i> in the fully hadronic final state in <i>pp</i> collisions at √<i>s</i>=13 TeV with the ATLAS detector

Abstract

<p>A search for <em>T</em> and <em>Y</em> vector-like quarks produced in proton-proton collisions at a centre-of-mass energy of 13 TeV and decaying into <em>Wb</em> in the fully hadronic final state is presented. The search uses 139 fb^{<em>−</em>1} of data collected by the ATLAS detector at the LHC from 2015 to 2018. The final state is characterised by a hadronically decaying <em>W</em> boson with large Lorentz boost and a <em>b</em>-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, <em>κ</em>. The observed lower limits on the masses of <em>Y</em> quarks with <em>κ</em> = 0<em>.</em>5 and <em>κ</em> = 0<em>.</em>7 are 2<em>.</em>0 TeV and 2<em>.</em>4 TeV, respectively. For <em>T</em> quarks, the observed mass limits are 1<em>.</em>4 TeV for <em>κ</em> = 0<em>.</em>5 and 1<em>.</em>9 TeV for <em>κ</em> = 0<em>.</em>7.<br></p>