BES Results on J/psi decays and Charmonium Transitions

TL;DR

This paper reports on detailed measurements of J/psi and psi(2S) decays, including branching fractions, resonance properties, and searches for exotic states, based on large data samples from the BESII experiment.

Contribution

It provides improved branching fraction measurements, studies of resonance structures, and sets limits on pentaquark signals in charmonium decays.

Findings

Observation of a broad sigma resonance with pole position.

No significant pentaquark (Theta(1540)) signal detected.

Identification of an enhancement near the p + Lambda mass threshold.

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.