Search for Production of Four Top Quarks in Final States with Same-sign or Multiple Leptons in Proton-proton Collisions at

The standard model (SM) production of four top quarks ( ) in proton-proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016-2018 data taking of the LHC, corresponds to an integrated luminosity of 137 at a center-of-mass energy of 13 . The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the signal are respectively 2.6 and 2.7 standard deviations, and the cross section is measured to be . The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, , yielding a limit of at confidence level, where is the SM value of . They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, . Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350-470 and 350-550 for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.