Measurement of Time-Dependent $CP$-Violating Asymmetries in $B^0\to \varphi K_S^0$, $K^{+}{K}^{-}{K}_S^0$, and ${\eta }^{\prime }{K}_S^0$ Decays

We present an improved measurement of $CP$-violation parameters in $B^0\to \varphi K_S^0$, $K^{+}{K}^{-}{K}_S^0$, and ${\eta }^{\prime }{K}_S^0$ decays based on a $140{\mathrm{f}\mathrm{b}}^{-1}$ data sample collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB energy-asymmetric $e^{+}{e}^{-}$ collider. One neutral $B$ meson is fully reconstructed in one of the specified decay channels, and the flavor of the accompanying $B$ meson is identified from its decay products. $CP$-violation parameters for each of the three modes are obtained from the asymmetries in the distributions of the proper-time intervals between the two $B$ decays. We find that the observed $CP$ asymmetry in the $B\to \varphi K_S^0$ decay differs from the standard model (SM) expectation by 3.5 standard deviations, while the other cases are consistent with the SM.