Measurement of the branching fraction of B →d (∗)πν at Belle using hadronic tagging in fully reconstructed events

We report a measurement of the branching fractions of the decays B→D(∗)πν. The analysis uses 772×106 BB. pairs produced in e+e-→(4S) data recorded by the Belle experiment at the KEKB asymmetric-energy e+e- collider. The tagging B meson in the decay is fully reconstructed in a hadronic decay mode. On the signal side, we reconstruct the decay B→D(∗)πν(=e,μ). The measured branching fractions are B(B+→D-π++ν)=[4.55±0.27 (stat.)±0.39 (syst.)]×10-3, B(B0→D.0π-+ν)=[4.05±0.36 (stat.)±0.41 (syst.)]×10-3, B(B+→D∗-π++ν)=[6.03±0.43 (stat.)±0.38 (syst.)]×10-3, and B(B0→D.∗0π-+ν)=[6.46±0.53 (stat.)±0.52 (syst.)]×10-3. These are in good agreement with the current world-average values.