A search for top decay into tau, neutrino and quark in top-antitop   production
  We present a search for top-antitop events with a tau lepton in the final state. The data sample corresponds to an integrated luminosity of 194/pb collected with the CDF II detector from proton-antiproton collisions at a center of mass energy of 1.96 TeV. We observe two events with an expected signal of 1.0+/-0.2 events and a background of 1.3+/-0.3 events. We determine a 95% confidence level upper limit on r_tau, the ratio of the measured rate of top->tau nu quark to the expectation, of 5.2. 
The CDF Collaboration