LAUSR

Abstract The cross section of top quark pair production is measured in the $$ \mathrm{t}\overline{\mathrm{t}}\to \left(\ell {\nu}_{\ell}\right)\left({\uptau}_{\mathrm{h}}{\nu}_{\uptau}\right)\mathrm{b}\overline{\mathrm{b}} $$ t t ¯ → ℓ ν ℓ τ h ν τ b b ¯ final state, where τh refers to the hadronic decays of the τ lepton, and ℓ 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 $$ \sqrt{s} $$ s = 13 TeV with the CMS detector. The measured cross section is $$ {\sigma}_{\mathrm{t}\overline{\mathrm{t}}} $$ σ t t ¯ = 781 ± 7 (stat) ± 62 (syst) ± 20 (lumi) pb, and the ratio of the partial width Γ(t → τντb) 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 $$ \mathrm{t}\overline{\mathrm{t}} $$ t t ¯ production cross section in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV that explicitly includes τ leptons. The ratio of the cross sections in the ℓτh and ℓℓ final states yields a value $$ {R}_{\ell {\uptau}_{\mathrm{h}}/\mathcal{ll}} $$ R ℓ τ h / ll = 0.973 ± 0.009 (stat) ± 0.066 (syst), consistent with lepton universality.