Search for tt¯ in final states with exactly one or two leptons using 140 fb−1 of pp collision data at √s=13 TeV with the ATLAS experiment

A search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb−1 of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of √s=13 TeV. Final states with either exactly one electron or muon, or exactly two leptons (ee, μμ or eμ), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b-hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4–5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z′ bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs.