Measurements of Branching Fractions and Time-DependentCP-Violating Asymmetries inB→η′KDecays

We present measurements of the $B\to {\eta }^{\prime }K$ branching fractions; for $B^{+}\to {\eta }^{\prime }{K}^{+}$ we measure also the time-integrated charge asymmetry ${\mathcal{A}}_{\mathrm{ch}}$, and for $B^0\to {\eta }^{\prime }{K}_S^0$ the time-dependent $CP$-violation parameters $S$ and $C$. The data sample corresponds to $232\times {10}^6$ $B\overline{B}$ pairs produced by $e^{+}{e}^{-}$ annihilation at the ${\rm Y}(4S)$. The results are $\mathcal{B}(B\to {\eta }^{\prime }{K}^{+})=(68.9\pm 2.0\pm 3.2)\times {10}^{-6}$, $\mathcal{B}(B^0\to {\eta }^{\prime }{K}^0)=(67.4\pm 3.3\pm 3.2)\times {10}^{-6}$, ${\mathcal{A}}_{\mathrm{ch}}=0.033\pm 0.028\pm 0.005$, $S=0.30\pm 0.14\pm 0.02$, and $C=-0.21\pm 0.10\pm 0.02$, where the first error quoted is statistical and the second is systematic.