Measurement of the Time-Dependent $CP$ Asymmetry in $B^0\to D_{CP}^{(*)}{h}^0$ Decays

We report a measurement of the time-dependent $CP$-asymmetry parameters $\mathcal{S}$ and $\mathcal{C}$ in color-suppressed $B^0\to D^{(*)0}{h}^0$ decays, where $h^0$ is a ${\pi }^0$, $\eta$, or $\omega$ meson, and the decays to one of the $CP$ eigenstates $K^{+}{K}^{-}$, $K_S^0{\pi }^0$, or $K_S^0\omega$. The data sample consists of $383\times {10}^6\mathit{{\rm Y}}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC. The results are $\mathcal{S}=-0.56\pm 0.23\pm 0.05$ and $\mathcal{C}=-0.23\pm 0.16\pm 0.04$, where the first error is statistical and the second is systematic.

Figure 1

The $m_{\mathrm{ES}}$ distributions with a fit to (a) the $CP$-even and (b) the $CP$-odd modes combined in the data. The solid curve represents the overall PDF projection, and the dashed curve represents the background.

Figure 2

The $\Delta t$ distributions and asymmetries for (a,b) $CP$-even and (c,d) $CP$-odd events in the signal region ($m_{\mathrm{ES}}>5.27\mathrm{GeV}/c^2$). In (a) and (c), the solid points with error bars and solid curve (open circles with error bars and dashed curve) are $B^0$-tagged (${\overline{B}}^0$-tagged) data points and $\Delta t$ projection curves. Shaded areas ($B^0$-tagged) and the dotted lines (${\overline{B}}^0$-tagged) are background distributions. In (b) and (d), the solid curve represents the combined fit result, and the dashed curve represents the result of the fits to $CP$-even and $CP$-odd modes separately.