Measurement of the branching ratio ofB¯→D(*)τ−ν¯τrelative toB¯→D(*)ℓ−ν¯ℓdecays with hadronic tagging at Belle

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Abstract

We report a measurement of the branching fraction ratios $R({D}^{(*)})$ of $\overline{B}\ensuremath{\rightarrow}{D}^{(*)}{\ensuremath{\tau}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ relative to $\overline{B}\ensuremath{\rightarrow}{D}^{(*)}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ (where $\ensuremath{\ell}=e$ or $\ensuremath{\mu}$) using the full Belle data sample of $772\ifmmode\times\else\texttimes\fi{}{10}^{6}B\overline{B}$ pairs collected at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The measured values are $R(D)=0.375\ifmmode\pm\else\textpm\fi{}0.064(\text{stat})\ifmmode\pm\else\textpm\fi{}0.026(\text{syst})$ and $R({D}^{*})=0.293\ifmmode\pm\else\textpm\fi{}0.038(\text{stat})\ifmmode\pm\else\textpm\fi{}0.015(\text{syst})$. The analysis uses hadronic reconstruction of the tag-side $B$ meson and purely leptonic $\ensuremath{\tau}$ decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.

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