Description
Semileptonic decays of $B$ mesons involving the high-mass $\tau$ lepton are sensitive probes for physics beyond the Standard Model. The relative rates of branching fractions $R(D) = \mathcal{B}(B \to D \tau \nu) / \mathcal{B}(B \to D l \nu)$ and $R(D^*) = \mathcal{B}(B \to D^* \tau \nu) / \mathcal{B}(B \to D^* l \nu)$ $(l=e,\mu)$ are independent of the CKM element $|V_{cb}|$ and of other theoretical uncertainties. Based on the 433 $\text{fb}^{-1}$ data collected at the $\Upsilon(4S)$ resonance by the BABAR detector at the PEP-II collider located at the SLAC National Accelerator Laboratory, we report a measurement of $R(D)$ and $R(D^{*})$ using semileptonic $B$-tagging and leptonic $\tau$ decays.
