Abstract: The cross section of top quark pair production is measured in the tt¯?(???)(?h??)bb¯ final state, where ?h refers to the hadronic decays of the ? lepton, and ? is either an electron or a muon. The data sample corresponds to an integrated luminosity of 35.9 fb?1 collected in proton-proton collisions at ?s = 13 TeV with the CMS detector. The measured cross section is ?tt¯ = 781 ± 7 (stat) ± 62 (syst) ± 20 (lumi) pb, and the ratio of the partial width ?(t ? ???b) to the total decay width of the top quark is measured to be 0.1050 ± 0.0009 (stat) ± 0.0071 (syst). This is the first measurement of the tt¯tt¯ production cross section in proton-proton collisions at ?s = 13 TeV that explicitly includes ? leptons. The ratio of the cross sections in the ??h and ?? final states yields a value R??h/ll = 0.973 ± 0.009 (stat) ± 0.066 (syst), consistent with lepton universality.

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