Search for heavy particles decaying into top-quark pairs using lepton-plus-jets events in proton–proton collisions at √s = 13 s = 13 TeV TeV with the ATLAS detector

A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton-proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider.The integrated luminosity of the data sample is 36.1 fb -1 .Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay.Jets identified as likely to contain b-hadrons are required to reduce the background from other Standard Model processes.The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation.No significant deviations from the Standard Model predictions are found.Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z bosons, Kaluza-Kein gluons and Kaluza-Klein gravitons that decay into top-quark pairs.