Measurement of BR(B0 -> Ds*+D*-) and Determination of the Ds+ -> phi pi+ Branching Fraction with a Partial-Reconstruction Method

Abstract

We present model-independent measurements of the branching fractions ${\cal B}(B^0\to D_s^{*+} D^{*-})$ and ${\cal B}(D_s^+ \to \phi \pi^+)$ based on 19.3 $\textup{fb}^{-1}$ of data collected by the $BABAR$ detector at the PEP-II $e^+e^-$ $B$ Factory. Neutral $B$-meson decays to the $D_s^{*+}D^{*-}$ final state are selected with a partial reconstruction of the $D_s^{*+}$; that is, only the $D^{*-}$ and the soft photon from the decay $D_s^{*+} \to \Ds \gamma$ are reconstructed. The branching fraction ${\cal B}(B^0\to D_s^{*+} D^{*-})$ is extracted from these event yields, while ${\cal B}(D_s^+ \to \phi \pi^+)$ is determined by combining this result with a previous measurement of the product ${\cal B}(B^0\to D_s^{*+} D^{*-}) \times {\cal B}(D_s^+ \to \phi \pi^+)$ with partial reconstruction of the $D^{*-}$. We obtain the following preliminary results: ${\cal B}(B^0\to D_s^{*+} D^{*-}) = (1.50 \pm 0.16 \pm 0.12)%,$ ${\cal B}(D_s^+ \to \phi \pi^+) = (4.7 \pm 0.6 \pm 0.8)%$ where the first error is statistical, and the second systematic.