Based on the full BABAR data sample, we report improved measurements of the ratios $\mathcal{R}(D^{(*)})=\mathcal{B}(\overline{B}\to D^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau })/\mathcal{B}(\overline{B}\to D^{(*)}{\ell }_{\ell }^{-}{\overline{\nu }}_{\ell })$, where $\ell$ is either $e$ or $\mu$. These ratios are sensitive to new physics contributions in the form of a charged Higgs boson. We measure $\mathcal{R}(D)=0.440\pm 0.058\pm 0.042$ and $\mathcal{R}(D^{*})=0.332\pm 0.024\pm 0.018$, which exceed the standard model expectations by $2.0\sigma$ and $2.7\sigma$, respectively. Taken together, our results disagree with these expectations at the $3.4\sigma$ level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.

• Received 31 May 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.101802