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 $\jpsi\to\ppp$, $\psip\ra \pi^0\J$, $\eta\J$, $\pi^0 \pi^0 J/\psi$, anything $J/\psi$, and $\psi(2S)\ar\gamma\chi_{c1},\gamma\chi_{c2}\ar\gamma\gamma\jpsi$. The decay $J/\psi \to \omega \pi ^+\pi ^-$ is studied. At low $\pi \pi$ mass, a large, broad peak due to the $\sigma$ is observed, and its pole position is determined. Results are presented on $\psi(2S)$ and $J/\psi$ hadronic decays to $K^0_SpK^-\bar n$ and $K^0_S\bar p K^+n$ final states. No significant $\Theta(1540)$ signal, the pentaquark candidate, is observed, and upper limits are set. An enhancement near the $m_p + M_{\Lambda}$ mass threshold is observed in the $p\bar{\Lambda}$ invariant mass spectrum from $J/\psi \to p K^- \bar{\Lambda} + c.c.$ 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 $\Gamma =90 \pm 35 (stat) \pm 9 (syst)$ MeV.