Measurement of the branching ratio of B^¯→ D^(∗)τ^- ν¯_τ relative to B^¯→ D^(∗)l⁻ν^¯_l decays with hadronic tagging at Belle

We report a measurement of the branching fraction ratios R(D(∗)) of B¯→D(∗)τ-ν¯τ relative to B¯→D(∗) -ν¯ (where =e or μ) using the full Belle data sample of 772×106BB¯ pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured values are R(D)=0.375±0.064(stat)±0.026(syst) and R(D∗)=0.293±0.038(stat)±0.015(syst). The analysis uses hadronic reconstruction of the tag-side B meson and purely leptonic τ decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.