Until its discovery in 1974, it was believed that only three kinds of quarks existed: up, down, and strange, but this particle proved the existence of a fourth.  
Like strange hyperons, it appears at high energies, and is relatively massive at 3.1 giga-electron volts per c squared, or about 3.5 atomic mass units.  Until its discovery in 1974, it was believed that only three kinds of quarks existed: up, down, and strange, but this particle proved the existence of a fourth.  Its name comes from the fact that two groups simultaneously discovered it: one at Stanford, and one at Brookhaven National Lab.  FTP, name this meson composed of a charm quark and a charm anti-quark.
Like strange hyperons, it appears at high energies, and is relatively massive at 3.1 giga-electron volts per c squared, or about 3.5 atomic mass units.  
J/psi particle