Search for pair-production of vector-like quarks in lepton plus jets final states containing at least one b-tagged jet using the Run 2 data from the ATLAS experiment

Abstract

A search is presented for the pair-production of heavy vector-like quarks in the lepton+jets final state using 140 fb-1 of proton-proton collisions at root s = 13 TeV collected with the ATLAS detector. The search is optimised for vector-like top-quarks (T) that decay into a W boson and a b-quark, with one W boson decaying leptonically and the other hadronically. Other vector-like quark flavours and decay modes are also considered. Events are selected with one high transverse-momentum electron or muon, large missing transverse momentum, a large-radius jet identified as a W boson, and multiple small-radius jets, at least one of which is b-tagged. Vector-like b-quarks with 100% branching ratio to W b are excluded at 95% CL for masses below 1700 GeV. These limits are also applied to vector-like Y-quarks, which decay exclusively into a W boson and a b-quark. Isospin singlets with B(T -> W b : Ht : Zt) = 1/2 : 1/4 : 1/4 are excluded for masses below 1360 GeV.