J/psi particle

noun1

1. •
   A subatomic particle with an unusually long lifetime (7.2 × 10⁻²¹ s) and a large mass (approx. 3.097 GeV/c²); a bound state of a charm quark and an anti-charm quark (the most common form of charmonium).

   • We report the observation of a heavy particle J, with mass m = 3.1 GeV and width approximately zero. — 1974