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

We present a measurement of time-dependent $CP$ asymmetries and an updated determination of the $CP$-odd fraction in the decay $B^0\to D^{*+}{D}^{*-}$ using a data sample of $88\times {10}^{6}B\overline{B}$ pairs collected by the BABAR detector at the PEP-II $B$ Factory at SLAC. We determine the $CP$-odd fraction to be $0.063\pm 0.055\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.009\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$. The time-dependent $CP$ asymmetry parameters $\mathrm{I}\mathrm{m}({\lambda }_{+})$ and $|{\lambda }_{+}|$ are determined to be $0.05\pm 0.29\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.10\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$ and $0.75\pm 0.19\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.02\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$, respectively. The standard model predicts these parameters to be $-\sin 2\beta$ and 1, respectively, in the absence of penguin diagram contributions.

Figure 1

Measured distribution of $\cos {\theta }_{\mathrm{t}\mathrm{r}}$ and fit results. The data points are from the region $m_{\mathrm{E}\mathrm{S}}>5.27\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}{c}^2$ and the solid line is the projection of the fit result in the same region. The dotted line represents the background component.

Figure 2

From top to bottom: Number $N_{B^0}$ $(N_{{\overline{B}}^0})$ of candidate events in the region $m_{\mathrm{E}\mathrm{S}}>5.27\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}{c}^2$ with a $B^0$ (${\overline{B}}^0$) tag, and the raw asymmetry $(N_{B^0}-N_{{\overline{B}}^0})/(N_{B^0}+N_{{\overline{B}}^0})$, as functions of $\mathrm{\Delta }t$. The solid curves represent the result of the combined fit to the full sample. The shaded regions represent the background contributions.