Measurement of the Branching Fraction, and Bounds on the CP-Violating Asymmetries, of Neutral $B$ Decays to $D^{*\pm }{D}^{\mp }$

We present measurements of the branching fraction and CP-violating asymmetries for neutral $B$ decays to $D^{*\pm }{D}^{\mp }$. The measurement uses a data sample of approximately $88\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $e^{+}\mathrm{\text{−}}{e}^{-}$ collider. By fully reconstructing the $D^{*\pm }{D}^{\mp }$ decay products, we measure the branching fraction to be $(8.8\pm 1.0\pm 1.3)\times {10}^{-4}$ and the time-integrated CP-violating asymmetry between the rates to $D^{*-}{D}^{+}$ and $D^{*+}{D}^{-}$ to be $\mathcal{A}=-0.03\pm 0.11\pm 0.05$. We also measure the time-dependent CP-violating asymmetry parameters to be $S_{-+}=-0.24\pm 0.69\pm 0.12$, $C_{-+}=-0.22\pm 0.37\pm 0.10$ for $B\to D^{*-}{D}^{+}$ and $S_{+-}=-0.82\pm 0.75\pm 0.14$, $C_{+-}=-0.47\pm 0.40\pm 0.12$ for $B\to D^{*+}{D}^{-}$. In each case, the first error is statistical and the second error is systematic.

Figure 1

The leading-order Feynman graphs for $B^0\to D^{*\pm }{D}^{\mp }$ decay: (a) tree diagram and (b) penguin diagram.

Figure 2

The $m_{\mathrm{E}\mathrm{S}}$ distributions of (a) $B\to D^{*-}{D}^{+}$ and (b) $B\to D^{*+}{D}^{-}$ candidates with $|\Delta E|<18\mathrm{M}\mathrm{e}\mathrm{V}$. The fit includes Gaussian distributions to model the signal and a small peaking background component, and an ARGUS function [11] to model the combinatoric background shape.

Figure 3

Distributions of $\mathrm{\Delta }t$ for $B\to D^{*+}{D}^{-}$ candidates in the signal region with (a) a $B^0$ tag ($N_{B^0}$), (b) with a ${\overline{B}}^0$ tag ($N_{{\overline{B}}^0}$), and (c) the raw asymmetry $(N_{B^0}-N_{{\overline{B}}^0})/(N_{B^0}+N_{{\overline{B}}^0})$. The solid curves are the fit projections in $\mathrm{\Delta }t$. The shaded regions represent the background contributions. Figures (d), (e), and (f) contain the corresponding information for $D^{*-}{D}^{+}$.