Evidence for the Rare Decay B -> J/psi eta K

Abstract

We report evidence for the $B$ meson decays, $B^\pm\to J/\psi \eta K^\pm$ and $B^0\to J/\psi \eta K^0_S$, using {90} million $B\bar B$ events collected at the $\ensuremath{\Upsilon{(4S)}}$ resonance with the \babar detector at the PEP-II $e^+ e^-$ asymmetric-energy storage ring. We obtain preliminary branching fractions in the charged and neutral channels of $(10.8\pm 2.3(stat.)\pm 2.4(syst.))\times 10^{-5}$ and $(8.4\pm 2.6(stat.)\pm 2.7(syst.))\times 10^{-5}$, respectively.