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An elementary particle with an unusually long lifetime or, from the Heisenberg uncertainty principle, with an extremely narrow width &Ggr; = 91.0 ± 3.2 keV, and a large mass m = 3096.916 ± 0.011 MeV. It is a bound state containing a charm quark and an anticharm quark. The discovery of the J/psi particle is one of the cornerstones of the standard model.
Since its discovery in 1974, more than 109 J/psi particles have been produced. More than 100 different decay modes and new particles radiating from the J/psi particle have been observed. The J/psi particle has been shown to be a bound state of charm quarks. The long lifetime of the J/psi results from its mass being less than the masses of particles which separately contain a charm and an anticharm quark. This situation permits the J/psi to decay only into noncharm quarks, and empirically this restriction was found to lead to a suppression of the decay rate resulting in a long lifetime and narrow width. The subsequent discovery of the b quark and the intermediate vector bosons Z0 and W±, and studies of Z0 decays into charm, b, and other quarks, show that the theory of the standard model is in complete agreement with experimental data to an accuracy of better than 1%. See Charm, Elementary particle, Intermediate vector boson, Quarks, Standard model, Upsilon particles