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

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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 √ 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 largeradius jet identified as a 𝑊 boson, and multiple small-radius jets, at least one of which is 𝑏-tagged.Vector-like 𝑇 -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.during the LHC Run 2. ATLAS has previously performed a search for pair-produced VLQs in the one lepton+jets final state using 36 fb -1 of Run 2 data which was optimised to the 𝑇 → 𝑊 𝑏 decay [13].That search excluded 𝑇