Observation of four-top-quark production in the multilepton final state with the ATLAS detector

The ATLAS collaboration
Aad, Georges , Abbott, Braden Keim , Abeling, Kira , Abicht, Nils Julius , Abidi, Haider , Aboulhorma, Asmaa , Abramowicz, Halina , Abreu, Henso , Abulaiti, Yiming , Abusleme Hoffman, A.C.
Eur.Phys.J.C 83 (2023) 496, 2023.

Abstract (data abstract)
A measurment is presented for four-top-quark production using an integrated luminosity of 140 fb\(^{-1}\) of proton--proton collision data at a centre-of-mass energy of 13 TeV 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 $22.5^{+6.6}_{-5.5}$ fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 6.1 (4.3) standard deviations and provides evidence for this process.

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