The discovery of Charm

In November 1974, two experiments [6,7] simultaneously announced the discovery of the $J/\psi$, a meson with a mass of about 3.1 and a narrow width which implied a much longer lifetime than other massive mesons. This particle was interpreted by some as the bound state of charmonium, ($\cq\cbq$). This hypothesis was later confirmed with the discovery of the and mesons [8,9] in 1976, although another experiment [10,11] had seen indications of so called ``open charm'' several years before the discovery of the $J/\psi$.

The discovery of the analogous $\bq\bbq$ resonance, $\Upsilon$ [12], followed shortly thereafter, indicating the existence of the third family of quarks. The discovery of the top quark [13], however, would be delayed for nearly 20 years due to its extremely large mass; so massive and short lived, in fact, that is does not combine into hadrons. Current evidence from measurements of the width of the strongly suggest that there are only three families of quarks [14].⁶