J/psi Meson

J/psi Meson

The J/ψ (J/Psi) meson is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium". The J/ψ is the first excited state of charmonium (i.e., the form of the charmonium with the second-smallest rest mass). The J/ψ has a rest mass of 3,096.9 MeV/c2, and a mean lifetime of 7.2×10−21 s. This lifetime was about a thousand times longer than expected.

Its discovery was made independently by two research groups, one at the Stanford Linear Accelerator Center, headed by Burton Richter, and one at the Brookhaven National Laboratory, headed by Samuel Ting at MIT. They discovered they had actually found the same particle, and both announced their discoveries on 11 November 1974. The importance of this discovery is highlighted by the fact that the subsequent, rapid changes in high-energy physics at the time have become collectively known as the "November Revolution". Richter and Ting were rewarded for their shared discovery with the 1976 Nobel Prize in Physics.