Measurement of the B0→D*-Ds*+ and Ds+→ϕπ+ branching fractions

We present measurements of the branching fractions B(B0→D*-Ds*+) and B(Ds+→ϕπ+), based on 123×106 Υ(4S)→BB̅ decays collected by the BABAR detector at the PEP-II asymmetric-energy e+e-  B factory. A partial reconstruction technique is used to measure B(B0→D*-Ds*+) and the decay chain is fully reconstructed to measure the branching fraction product B(B0→D*-Ds*+)×B(Ds+→ϕπ+). Comparing these two measurements provides a model-independent determination of the Ds+→ϕπ+ branching fraction. We obtain B(B0→D*-Ds*+)=(1.88±0.09±0.17)% and B(Ds+→ϕπ+)=(4.81±0.52±0.38)%, where the first uncertainties are statistical and the second systematic.