Search for the $CP$-Violating Decays $\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}{B}^{0}{\overline{B}}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}_{S}^{0}+J/\ensuremath{\psi}({\ensuremath{\eta}}_{c}){K}_{S}^{0}$

Search for the $C P$ -Violating Decays $Υ (4 S) \to B^{0} {\bar{B}}^{0} \to J / ψ K_{S}^{0} + J / ψ (η_{c}) K_{S}^{0}$

O. Tajima et al. (Belle Collaboration)

Phys. Rev. Lett. 99, 211601 – Published 20 November 2007

Abstract

We report the first search for $C P$ -violating decays of the $Υ (4 S)$ using a data sample that contains $535 \times 10^{6}$ $Υ (4 S)$ mesons with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. A partial reconstruction technique is employed to enhance the signal sensitivity. No significant signals were observed. We obtain an upper limit of $4 \times 10^{- 7}$ at the 90% confidence level for the branching fractions of the $C P$ violating modes, $Υ (4 S) \to B^{0} {\bar{B}}^{0} \to J / ψ K_{S}^{0} + J / ψ (η_{c}) K_{S}^{0}$ . Extrapolating the result, we find that an observation with $5 σ$ significance is expected with a $30 {ab}^{- 1}$ data sample, which is within the reach of a future super $B$ factory.