Measurement of CP-Violating Parameters in $B\to {\eta }^{\prime }K$ Decays

Abstract

We present measurements of CP-violating parameters in $B^0(\bar{B}{}^0)\to {\eta }^{\prime }{K}_S^0$ and $B^{\pm }\to {\eta }^{\prime }{K}^{\pm }$ decays based on a 41.8 fb${}^{-1}$ data sample collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We fully reconstruct one neutral $B$ meson as a $B^0(\bar{B}{}^0)\to {\eta }^{\prime }{K}_S^0$ CP eigenstate and identify the flavor of the accompanying $B$ from its decay products. From the distribution of time intervals between pairs of $B$ meson decay points, we obtain the CP-violating asymmetry parameters ${\mathcal{S}}_{{\eta }^{\prime }{K}_S^0}=0.28\pm 0.55(stat{)}_{-0.08}^{+0.07}(syst)$, and ${\mathcal{A}}_{{\eta }^{\prime }{K}_S^0}=0.13\pm 0.32(stat{)}_{-0.06}^{+0.09}(syst)$. We also reconstruct charged $B^{\pm }\to {\eta }^{\prime }{K}^{\pm }$ decays and determine a direct-CP violating asymmetry value of ${\mathcal{A}}_{{\eta }^{\prime }{K}^{\pm }}=(-1.5\pm 7.0(stat)\pm 0.9(syst))$.

Revised version: 16 pages, 3 figures, 1 table submitted to Phys. Lett. B