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 anti
charm 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).