BES Results on J/psi decays and Charmonium Transitions

Abstract

Results are reported based on samples of 58 million $\jpsi$ and 14 million $\psip$ decays obtained by the BESII experiment. Improved branching fraction measurements are determined, including branching fractions for $\jpsi\to\ppp$, $\psip\ra π^0\J$, $η\J$, $π^0 π^0 J/ψ$, anything $J/ψ$, and $ψ(2S)\arγχ_{c1},γχ_{c2}\arγγ\jpsi$. The decay $J/ψ\to ωπ^+π^-$ is studied. At low $ππ$ mass, a large, broad peak due to the $σ$ is observed, and its pole position is determined. Results are presented on $ψ(2S)$ and $J/ψ$ hadronic decays to $K^0_SpK^-\bar n$ and $K^0_S\bar p K^+n$ final states. No significant $Θ(1540)$ signal, the pentaquark candidate, is observed, and upper limits are set. An enhancement near the $m_p + M_Λ$ mass threshold is observed in the $p\barΛ$ invariant mass spectrum from $J/ψ\to p K^- \barΛ + c.c.$ decays. It can be fit with an S-wave Breit-Wigner resonance with a mass $m=2075\pm 12 (stat) \pm 5 (syst)$ MeV and a width of $Γ=90 \pm 35 (stat) \pm 9 (syst)$ MeV.