Search for pair-produced vectorlike quarks coupling to light quarks in the lepton plus jets final state using 13 TeV pp collisions with the ATLAS detector

A search is presented for the pair-production of heavy vector-like quarks (VLQs) that each decay into a W boson and a light quark. This study focuses on events where one $W$ boson decays into leptons and the other into hadrons. The search analyzed 140 fb^-1 of pp collision data with sqrt(s) = 13 TeV, recorded by the ATLAS detector from 2015 to 2018 during Run 2 of the Large Hadron Collider. The final state is characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, multiple small-radius jets, and a single large-radius jet identified as originating from the hadronic decay of a boosted W boson. With higher center-of-mass energy and integrated luminosity than in the Run 1 search, and improved analysis tools, this analysis excludes VLQs (Q) with masses below 1530 GeV at 95% CL for the branching ratio B(Q -> Wq) = 1, an improvement of 840 GeV on the previous ATLAS limit.