Its hadronic decays proceed primarily through a three-gluon intermediate state, suppressing their rate dramatically and making it a very narrow resonance.  
The earliest extensive studies of this particle were done with the Mark I, II, and III experiments.  Its hadronic decays proceed primarily through a three-gluon intermediate state, suppressing their rate dramatically and making it a very narrow resonance.  It can decay through a M1 transition to the eta sub c.  At 3.1 giga-electron volts, it is the lightest member of its family with the same quantum numbers as the photon.  It is often easiest to observe in its dimuon and dielectron decay modes.  Its simultaneous discovery in 1974 by groups at Stanford and Brookhaven led to its uniquely double-barreled name.  FTP, identify this particle, the lightest vector bound state of a charm and anticharm quark.
The earliest extensive studies of this particle were done with the Mark I, II, and III experiments.  
J/psi particle (accept "psi prime" before 3.1 GeV)