
The J/ψ particle is a charm-anticharm meson whose decays are studied to probe physics beyond the Standard Model.The J/ψ particle is a meson — a particle made of a quark and an antiquark — specifically a charm quark bound to its antiparticle, the anticharm quark. It was discovered independently in 1974 by two teams, one led by Samuel Ting at Brookhaven and the other by Burton Richter at SLAC, in a landmark event that reshaped particle physics. The J/ψ is notable for its unusually long lifetime for a particle of its mass, which arises because its decay is suppressed by a quantum mechanical rule known as the OZI rule. This longevity makes it an excellent laboratory for studying the strong force and for searching for rare processes that could hint at new physics beyond the Standard Model.
The J/ψ was discovered in November 1974, independently by Samuel Ting's group at Brookhaven National Laboratory (who called it 'J') and Burton Richter's group at SLAC (who called it 'ψ'). The discovery was announced on November 11, 1974, and was so rapid and impactful that it became known as the 'November Revolution' in particle physics. Ting and Richter shared the 1976 Nobel Prize in Physics for the discovery.
The J/ψ is produced in high-energy particle collisions, such as electron-positron annihilation, where the energy converts into the charm-anticharm pair. Its decays are studied by detecting the particles it produces, such as muons, electrons, or photons. Because the J/ψ is relatively heavy (about 3.1 GeV/c²), it can decay into many different final states, and the relative rates of these decays — the branching fractions — are sensitive to the influence of new, undiscovered particles that might appear in quantum loops. By measuring these rates with high precision, physicists can look for deviations from Standard Model predictions, which would signal new physics.
The J/ψ is used as a calibration tool and a probe in particle physics experiments, such as those at CERN's LHC and at B-factories, to test the Standard Model and search for dark matter candidates through invisible decays.
The J/ψ's discovery was so unexpected that it was nicknamed the 'November Revolution' because it overturned the then-prevailing theory of quarks, which had predicted that charm quarks would be much heavier.





