A search for t→τνq in tt¯ production

We present a search for t t ¯ events with a tau lepton in the final state. The data sample corresponds to an integrated luminosity of 194 pb −1 collected with the CDF II detector from p p ¯ 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 τ , the ratio of the measured rate of t → τ ν q to the expectation, of 5.2.