Charmonium

Charmonium is a family of mesons made from a charm quark and a charm antiquark. Its spectrum provides a laboratory for studying the strong interaction between heavy quarks.

Charm quark: A quark of the second generation, with electric charge +2/3 and a mass far greater than up and down quarks. It is the heavy constituent shared by every charmonium state.
Charmonium spectrum: The measured set of charmonium masses, quantum numbers, and decay properties. Its level structure tests models of the charm–anticharm interaction.
J/ψ meson: A narrow vector meson composed of a charm quark and a charm antiquark. Its 1974 discovery revealed a remarkably long-lived charmonium state.
J/ψ discovery: The 1974 observation of a narrow particle now identified as the J/ψ meson. The discovery supplied the first decisive evidence for bound charm and anticharm.
Meson: A hadron made primarily of one quark and one antiquark. Charmonium belongs to this broader family of quark–antiquark particles.
Color confinement: The absence of isolated color-charged particles at low energies in quantum chromodynamics. It prevents the charm quark and antiquark from appearing as free particles.
ψ(2S): The first radially excited vector charmonium state, discovered shortly after the J/ψ. Its mass and decay patterns helped establish the charmonium level scheme.
Brookhaven National Laboratory: A United States research laboratory where the AGS accelerator operates. The J/ψ was observed there by the experiment led by Samuel Ting’s group.
Quantum chromodynamics: The theory describing the strong interaction between quarks and gluons. It governs the binding and interactions of charmonium’s constituents.
Spin: An intrinsic form of angular momentum carried by quantum particles. Quark spins distinguish charmonium states such as the J/ψ and ηc.

Linked from 7 pages