We present an analysis of top-antitop quark production and decay into a tau lepton, tau neutrino, and bottom quark using data from $9{\mathrm{fb}}^{-1}$ of integrated luminosity at the Collider Detector at Fermilab. Dilepton events, where one lepton is an energetic electron or muon and the other a hadronically decaying tau lepton, originating from proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$, are used. A top-antitop quark production cross section of $8.1\pm 2.1\mathrm{pb}$ is measured, assuming standard-model top quark decays. By separately identifying for the first time the single-tau and the ditau components, we measure the branching fraction of the top quark into the tau lepton, tau neutrino, and bottom quark to be $(9.6\pm 2.8)\%$. The branching fraction of top quark decays into a charged Higgs boson and a bottom quark, which would imply violation of lepton universality, is limited to be less than 5.9% at a 95% confidence level [for $\mathcal{B}({\mathrm{H}}^{-}\to \tau \overline{\nu })=1$].

• Received 26 February 2014

DOI:https://doi.org/10.1103/PhysRevD.89.091101