Improved 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 the $CP$-odd fraction and the time-dependent $CP$ asymmetries in the decay $B^0\to D^{*+}{D}^{*-}$ using $(383\pm 4)\times {10}^{6}B\overline{B}$ pairs collected with the BABAR detector. We determine the $CP$-odd fraction to be $0.143\pm 0.034(\mathrm{stat})\pm 0.008(\mathrm{syst})$. The time-dependent $CP$ asymmetry parameters are determined to be $C_{+}=-0.05\pm 0.14(\mathrm{stat})\pm 0.02(\mathrm{syst})$ and $S_{+}=-0.72\pm 0.19(\mathrm{stat})\pm 0.05(\mathrm{syst})$. The nonzero value of the measured $S_{+}$ indicates the evidence of $CP$ violation at the $3.7\sigma$ confidence level.

Figure 1

Depiction of the $B^0\to D^{*+}{D}^{*-}$ decay in the transversity basis. The three transversity angles are defined in the text.

Figure 2

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

Figure 3

The distribution in $\Delta t$ of the yield in the region $m_{\mathrm{ES}}>5.27\mathrm{GeV}/c^2$ for $B^0({\overline{B}}^0)$ tagged candidates (a) and the raw asymmetry $(N_{B^0}-N_{{\overline{B}}^0})/(N_{B^0}+N_{{\overline{B}}^0})$, as functions of $\Delta t$ (b). In (a), the solid (dashed) curves represent the fit to the data for $B^0({\overline{B}}^0)$ tags.