Evidence for four-top quark production in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The production of four top quarks (ttt¯ t)¯ is studied with LHC proton-proton collision data samples
collected by the CMS experiment at a center-of-mass energy of 13 TeV, and corresponding to integrated
luminosities of up to 138 fb−1. Events that have no leptons (all-hadronic), one lepton, or two oppositesign leptons (where lepton refers only to prompt electrons or prompt muons) are considered. This is
the first ttt¯ t measurement ¯ that includes the all-hadronic final state. The observed significance of the ttt¯ t¯
signal in these final states of 3.9 standard deviations (1.5 expected) provides evidence for ttt¯ t production, ¯
with a measured cross section of 36+12
−11 fb. Combined with earlier CMS results in other final states, the
signal significance is 4.0 standard deviations (3.2 expected). The combination returns an observed cross
section of 17 ± 4 (stat) ± 3 (syst) fb, which is consistent with the standard model prediction.