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

TL;DR

This paper reports the first measurement of the top quark pair production cross section at 13 TeV including tau leptons, providing insights into top quark decays and testing lepton universality.

Contribution

It presents the first measurement of the top quark pair production cross section in final states with tau leptons at 13 TeV, using CMS data.

Findings

Measured cross section: 781 ± 7 (stat) ± 62 (syst) ± 20 (lum) pb.

Ratio of partial width to total width: 0.1050 ± 0.0009 (stat) ± 0.0071 (syst).

Cross section ratio in different final states: 0.973 ± 0.009 (stat) ± 0.066 (syst).

Abstract

The cross section of top quark pair production is measured in the $\mathrm{t\bar{t}}$ $\to$ $(\ell\nu_{\ell})(\tau_\mathrm{h}\nu_{\tau})\mathrm{b\bar{b}}$ 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 $\sigma_{\mathrm{t\bar{t}}} =$ 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 $\mathrm{t\bar{t}}$ 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.