N* Resonances in e+e- Collisions at Bepc

Abstract

$J/\Psi$ particles are abundantly produced at the Beijing Electron Positron Collider (BEPC). The $J/\Psi$ decays provide an excellent place for studying $N^{\ast }$ resonances. For $J/\Psi \to \bar{N}N\pi$ and $\bar{N}N\pi \pi$, the $\pi N$ and $\pi \pi N$ systems are limited to be pure isospin 1/2 due to isospin conservation. This is a big advantage in studying $N^{\ast }$ resonances from $J/\Psi$ decays, compared with $\pi N$ and $\gamma N$ experiments which suffer difficulty on the isospin decomposition of 1/2 and 3/2. All other $N^{\ast }$ decay channels which are presently under investigation at CEBAF(JLab, USA), ELSA(Bonn,Germany) and GRAAL(Grenoble, France) with real photon or space-like virtual photon can also be studied at BEPC complementally with the time-like virtual photon. The process $J/\Psi \to \bar{N}{N}^{\ast }$ or $N{\bar{N}}^{\ast }$ provides a new way to probe the internal structure of the $N^{\ast }$ resonances. The recent results and outlook of our new $N^{\ast }$ program at BEPC are presented.

Postscript file, 8 pages. Talk given at the International Workshop on the Physics of Excited Nucleons (NSTAR2000), Jefferson Lab, Virginia, USA, February 2000