Çetin, Serkant AliÇelebi, Emre2021-05-072021-05-072020-111434-6044https://hdl.handle.net/11411/3648https://doi.org/10.1140/epjc/s10052-020-08509-3A 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. The four-top-quark production cross section is measured to be 24-6+7 fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.eninfo:eu-repo/semantics/openAccessArticle2-s2.0-8509651688710.1140/epjc/s10052-020-08509-3Q1WOS:000595710000001