Evidence for an Excess of $\overline{B}\to D^{(*)}{\tau }^{-}{\overline{\nu }}_{\tau }$ Decays

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.

Figure 1

Comparison of the data and the fit projections for the four $D^{(*)}\ell$ samples. The insets show the $|{\mathit{p}}_{\ell }^{*}|$ projections for $m_{\mathrm{miss}}^2>1{\mathrm{GeV}}^2$, which excludes most of the normalization modes. In the background component, the region above the dashed line corresponds to charge cross-feed, and the region below corresponds to continuum and $B\overline{B}$.

Figure 2

Comparison of the results of this analysis (light gray, blue) with predictions that include a charged Higgs boson of type II 2HDM (dark gray, red). The SM corresponds to $\tan \beta /m_{H^{+}}=0$.