Improved Measurement of $CP$ Violation in Neutral $B$ Decays to $c\overline{c}s$

We present updated measurements of time-dependent $CP$ asymmetries in fully-reconstructed neutral $B$ decays to several $CP$ eigenstates containing a charmonium meson. The measurements use a data sample of $(383\pm 4)\times {10}^6\mathit{{\rm Y}}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II $B$ factory. We determine $\sin 2\beta =0.714\pm 0.032(\mathrm{stat})\pm 0.018(\mathrm{syst})$ and $|\lambda |=0.952\pm 0.022(\mathrm{stat})\pm 0.017(\mathrm{syst})$.

Figure 1

Distributions for $B_{CP}$ and $B_{\mathrm{flav}}$ candidates satisfying the tagging and vertexing requirements: (a) $m_{\mathrm{ES}}$ for the final states $J/\psi K_S^0$, $\psi (2S)K_S^0$, ${\chi }_{c1}{K}_S^0$, and ${\eta }_c{K}_S^0$, (b) $\Delta E$ for the final state $J/\psi K_L^0$, (c) $m_{\mathrm{ES}}$ for $J/\psi K^{*0}(K^{*0}\to K_S^0{\pi }^0)$, and (d) $m_{\mathrm{ES}}$ for the $B_{\mathrm{flav}}$ sample. In each plot, the shaded region is the estimated background contribution.

Figure 2

(a) Number of ${\eta }_f=-1$ candidates ($J/\psi K_S^0$, $\psi (2S)K_S^0$, ${\chi }_{c1}{K}_S^0$, and ${\eta }_c{K}_S^0$) in the signal region with a $B^0$ tag ($N_{B^0}$) and with a ${\overline{B}}^0$ tag ($N_{{\overline{B}}^0}$), and (b) the raw asymmetry, $(N_{B^0}-N_{{\overline{B}}^0})/(N_{B^0}+N_{{\overline{B}}^0})$, as functions of $\Delta t$. Figures (c) and (d) are the corresponding distributions for the ${\eta }_f=+1$ mode $J/\psi K_L^0$. To enhance the signal component, all distributions exclude the other tagging category. The solid (dashed) curves represent the fit projections in $\Delta t$ for $B^0$ (${\overline{B}}^0$) tags. The shaded regions represent the estimated background contributions.