J/ψ meson

The J/ψ meson is a neutral, short-lived bound state of a charm quark and an anticharm quark. Its 1974 discovery revealed a new heavy-quark family and helped establish the quark model.

Charmonium: The family of bound states formed by a charm quark and an anticharm quark. The J/ψ is charmonium’s ground state.
November Revolution: The 1974 upheaval in particle physics triggered by discoveries of the J/ψ and related particles. The J/ψ’s unexpected mass and narrow width made its discovery a turning point.
Electron–positron annihilation: A process in which an electron and positron convert their energy into other particles. The J/ψ can form as a resonance when colliding beams reach its mass.
Quarkonium suppression: A reduction in heavy quark–antiquark bound-state yields in high-energy nuclear collisions. Suppressed J/ψ production was proposed as a signal of deconfined quark–gluon matter.
Charm quark: A quark flavor with electric charge +2/3 and a mass much greater than those of up and down quarks. One charm quark supplies each constituent pair in the J/ψ.
Brookhaven National Laboratory: A United States research laboratory where particle physicists discovered the J particle in 1974. Samuel Ting’s team observed the J/ψ in proton–beryllium collisions there.
J/ψ decay: The transformation of a J/ψ meson into lighter particles through strong or electromagnetic interactions. Its unusually narrow width follows from suppressed annihilation into gluons.
Quark–gluon plasma: A high-temperature state of matter in which quarks and gluons are not confined inside hadrons. J/ψ yields and momentum distributions help study this state in nuclear collisions.
Quantum chromodynamics: The theory of the strong interaction between quarks and gluons. It binds the J/ψ’s charm and anticharm constituents.
Stanford Linear Accelerator Center: A California laboratory that housed the SPEAR electron–positron collider. Burton Richter’s team independently found the ψ resonance at SPEAR.

Linked from 9 pages