Observation of mixing-inducedCPviolation in the neutralBmeson system
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Abstract
This article describes an observation of mixing-induced $\mathrm{CP}$ violation and a measurement of the $\mathrm{CP}$ violation parameter, $\mathrm{sin}2{\ensuremath{\varphi}}_{1},$ with the Belle detector at the KEKB asymmetric ${e}^{+}{e}^{\ensuremath{-}}$ collider. Using a data sample of $29.1 {\mathrm{fb}}^{\ensuremath{-}1}$ recorded on the $\ensuremath{\Upsilon}(4S)$ resonance that contains 31.3 million $B\overline{B}$ pairs, we reconstruct decays of neutral B mesons to the following $\mathrm{CP}$ eigenstates: $J/\ensuremath{\psi}{K}_{S}^{0},$ $\ensuremath{\psi}{(2S)K}_{S}^{0},$ ${\ensuremath{\chi}}_{c1}{K}_{S}^{0},$ ${\ensuremath{\eta}}_{c}{K}_{S}^{0},$ $J/\ensuremath{\psi}{K}_{L}^{0}$ and $J/\ensuremath{\psi}{K}^{*0}.$ The flavor of the accompanying B meson is identified by combining information from primary and secondary leptons, ${K}^{\ifmmode\pm\else\textpm\fi{}}$ mesons, $\ensuremath{\Lambda}$ baryons, slow and fast pions. The proper-time interval between the two B meson decays is determined from the distance between the two decay vertices measured with a silicon vertex detector. The result $\mathrm{sin}2{\ensuremath{\varphi}}_{1}=0.99\ifmmode\pm\else\textpm\fi{}0.14(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{syst})$ is obtained by applying a maximum likelihood fit to the 1137 candidate events. We conclude that there is large $\mathrm{CP}$ violation in the neutral B meson system. A zero value for $\mathrm{sin}2{\ensuremath{\varphi}}_{1}$ is ruled out by more than six standard deviations.