Measurement of the top quark pair production cross section in dilepton final states containing one $\tau$ lepton in pp collisions at $\sqrt{s}=$ 13 TeV

Abstract

The cross section of top quark pair production is measured in the $\mathrm{t}\bar{\mathrm{t}}$ $\to$ $(\ell {\nu }_{\ell })({\tau }_{\mathrm{h}}{\nu }_{\tau })\mathrm{b}\bar{\mathrm{b}}$ final state, where ${\tau }_{\mathrm{h}}$ refers to the hadronic decays of the $\tau$ lepton, and $\ell$ 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 $\sqrt{s}=$ 13 TeV with the CMS detector. The measured cross section is ${\sigma }_{\mathrm{t}\bar{\mathrm{t}}}=$ 781 $\pm$ 7 (stat) $\pm$ 62 (syst) $\pm$ 20 (lum) pb, and the ratio of the partial width $\Gamma ($t $\to$ $\tau {\nu }_{\tau }$b) to the total decay width of the top quark is measured to be 0.1050 $\pm$ 0.0009 (stat) $\pm$ 0.0071 (syst). This is the first measurement of the $\mathrm{t}\bar{\mathrm{t}}$ production cross section in proton-proton collisions at $\sqrt{s}=$ 13 TeV that explicitly includes $\tau$ leptons. The ratio of the cross sections in the $\ell {\tau }_{\mathrm{h}}$ and $\ell \ell$ final states yields a value $R_{\ell {\tau }_{\mathrm{h}}/\ell \ell }=$ 0.973 $\pm$ 0.009 (stat) $\pm$ 0.066 (syst), consistent with lepton universality.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/TOP-18-005 (CMS Public Pages)