Search for production of four top quarks in final states with same-sign or multiple leptons in proton–proton collisions at s√=13 TeV

The standard model (SM) production of four top quarks (tt¯tt¯) 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 137fb−1 at a center-of-mass energy of 13TeV. 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 tt¯tt¯ signal are respectively 2.6 and 2.7 standard deviations, and the tt¯tt¯ cross section is measured to be 12.6+5.8−5.2fb. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, yt, yielding a limit of |yt/ySMt|<1.7 at 95% confidence level, where ySMt is the SM value of yt. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework, H^