Study of Charmonium Decays into Baryon-Antibaryon Pairs

Abstract

We study the baryonic charmonium decays of $B$ mesons, $B^{+}\to {\eta }_c{K}^{+}$ and $B^{+}\to J/\psi K^{+}$, where ${\eta }_c$ and $J/\psi$ subsequently decay into a $p\bar{p}$ or $\Lambda \bar{\Lambda }$ pair. The charmonium produced in the above $B$ meson decays is fully polarized. The polar angular distributions of the baryon-antibaryon pairs are presented, along with fit results to a $1+{\alpha }_B{\cos }^2\theta$ parametrization. Comparisons are made with the results from $e^{+}{e}^{-}\to J/\psi$ formation experiments. We also report the firstobservation of $η_c \to Λ\bar\Lambdar$. The measured branching fraction is $\mathcal{B}({\eta }_c\to \Lambda \bar{\Lambda })=(0.87_{-0.21}^{+0.24}\pm 0.14\pm 0.27)\times 10^{-3}$. This study is based on a $357f{b}^{-1}$ data sample recorded on the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

arXiv comment11 pagpes, 6 figures, for LP2005 and EPS2005