Improved measurement of mixing-induced<i>CP</i>violation in the neutral<i>B</i>meson system

Abstract

We present an improved measurement of the standard model CP violation parameter $\mathrm{sin}2{\ensuremath{\varphi}}_{1}$ (also known as $\mathrm{sin}2\ensuremath{\beta})$ based on a sample of $85\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected at the $\ensuremath{\Upsilon}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. One neutral B meson is reconstructed in a $J/\ensuremath{\psi}{K}_{S}^{0},$ $\ensuremath{\psi}{(2S)K}_{S}^{0},$ ${\ensuremath{\chi}}_{c1}{K}_{S}^{0},$ ${\ensuremath{\eta}}_{c}{K}_{S}^{0},$ $J/\ensuremath{\psi}{K}^{*0},$ or $J/\ensuremath{\psi}{K}_{L}^{0}$ CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time interval between the two B meson decay points, we obtain $\mathrm{sin}2{\ensuremath{\varphi}}_{1}=0.719\ifmmode\pm\else\textpm\fi{}0.074(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.035(\mathrm{syst}).$