Ricerc@Sapienza

Corrections for five figures and six tables are noted for the paper, which do not affect the conclusions reported.

A search is presented for four-top-quark production using an integrated luminosity of 139 fb- 1 of proton–proton collision data at a centre-of-mass energy of 13TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds.