Speaker
Fergus Wilson
(Science and Technology Facilities Council STFC (GB))
Description
Semileptonic decays of $B$ mesons involving $\tau$ leptons are sensitive probes for physics beyond the Standard Model. The relative rates of the branching fractions $R(D) = \mathcal{B}(B \to D \tau \nu) / \mathcal{B}(B \to D \ell \nu)$ and $R(D^*) = \mathcal{B}(B \to D^* \tau \nu) / \mathcal{B}(B \to D^* \ell \nu)$, where $(\ell=e,\mu)$ are independent of the CKM element $|V_{cb}|$ and many theoretical uncertainties. We report a measurement of ratios $R(D)$ and $R(D^{*})$ using semileptonic $B$-tagging and leptonic $\tau$ decays using the 433 fb$^{-1}$ data collected at the $\Upsilon(4S)$ resonance by the $BABAR$ detector at the PEP-II collider located at the SLAC National Accelerator Laboratory.