Measurement of Time-Dependent $CP$ Asymmetries and the $CP$-Odd Fraction in the Decay $B^0\to D^{*}+D^{*-}$

We present an updated measurement of time-dependent $CP$ asymmetries and the $CP$-odd fraction in the decay $B^0\to D^{*+}{D}^{*-}$ using $232\times {10}^{6}B\overline{B}$ pairs collected by the BABAR detector at the SLAC PEP-II $B$ factory. We determine the $CP$-odd fraction to be $0.125\pm 0.044(\mathrm{stat})\pm 0.007(\mathrm{syst})$. The time-dependent $CP$ asymmetry parameters $C_{+}$ and $S_{+}$ are determined to be $0.06\pm 0.17(\mathrm{stat})\pm 0.03(\mathrm{syst})$ and $-0.75\pm 0.25(\mathrm{stat})\pm 0.03(\mathrm{syst})$, respectively. The standard model predicts these parameters to be 0 and $-\sin 2\beta$, respectively, in the absence of penguin amplitude contributions.

Figure 1

Measured distribution of $m_{\mathrm{ES}}$ (left) and of $\cos {\theta }_{\mathrm{tr}}$ in the region $m_{\mathrm{ES}}>5.27\mathrm{GeV}/c^2$ (right). The solid line is the projection of the fit result. The dotted line represents the background component.

Figure 2

From top to bottom: the distribution of $\Delta t$ in the region $m_{\mathrm{ES}}>5.27\mathrm{GeV}/c^2$ for $B^0$ (${\overline{B}}^0$) tag candidates, and the raw asymmetry $(N_{B^0}-N_{{\overline{B}}^0})/(N_{B^0}+N_{{\overline{B}}^0})$, as functions of $\Delta t$. In the upper plot the solid (dashed) curves represent the fit projections in $\Delta t$ for $B^0$ (${\overline{B}}^0$) tags.