Measurement of the branching fractions for B- → D (*)+π-ℓ-v̄ℓ and B̄0 → D(*)0π+ℓ -v̄ℓ

We report on a measurement of the branching fractions for B- → D()+π- ℓ -v̄ℓ and B̄0 → D ()0π+ℓ-v̄ℓ with 275 × 106 BB̄ events collected at the γ(4S) resonance with the Belle detector at KEKB. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain B(B- → D+π- ℓ-v̄ℓ = (0.54±0.07(stat)±0.07(syst)±0.06(BR))× 10 -2, B(B- → D()+π- ℓ-v̄ℓ = (0.67 ±0.11(stat) ±0.09(syst) ±0.03(BR)) × 10-2, B(B̄0 → D0π+ ℓ -v̄ℓ) = (0.33 ±0.06(stat) ± 0.06(syst) ±0.03(BR)) × 10-2, B(B̄0 → D()0π+ℓ -v̄ℓ) = (0.65 ±0.12(stat) ± 0.08(syst) ±0.05(BR)) × 10-2, where the third error comes from the error on B̄ → D()ℓ -v̄ℓ decays. Contributions from B0 → D()+ℓ-v̄ℓ decays are excluded in the measurement of B̄0 → D0π +ℓ-v̄ℓ. © 2005 The American Physical Society.