The quarkoniums are mesons each made of a quark and the corresponding antiquark. Is the ideal system for studying the strong interquark color force.

The most important example of this in the history of particle physics is the J/Psi particle (made up of a charm and anticharm quark), discovered in November 1974 at a center-of-mass-energy of 3.1 GeV/c^2. Normally, quarks in hadrons move with a speed near that of light, and calculations of their properties must be done using the complicated equations of relativistic quantum mechanics. But this system proved particularly useful because it the charm quark is massive enough so that in this J/Psi bound state, they're moving slow enough so you can neglect relativistic effects. In this J/Psi "charmonium" system, the math is much easier, and the details of the interquark force are easier to study.

This 'November Revolution' of 1974 led particle physics in new directions. Feynman's QED was extended, and Quantum Chromodynamics (QCD) came of age. The discovery of the charmed quark in the J/Psi system stimmulated the search for yet heavier quarks, and in 1977, the bottom quark was found at Fermilab in the analogous quarkonium system, bottomonium (the Upsilon particle, m = 9.46 GeV/c^2).

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