Charmonium

In high energy physics, a charmonium (plural charmonia) is a flavorless meson constituted by a charm quark and an anti-charm quark. Different charmonium states can be discriminated in function of its quantum numbers: S, L, and J (or equivalently, J, P and C).

Charmonium states J^PC = 1⁻⁻ can be produced directly from electron-positron collisions —as they have the same quantum numbers as the photon— via the process:

Non-1⁻⁻ forms are then usually studied from radiative decays:

Alternatively, proton-antiproton annhilation allows all charmonium states to be be produced.

List of some charmonium states

In the following table, the same particle can be named with the spectroscopic notation or with its mass. In some cases excitation series are used: Ψ' is the first excitation of Ψ (for historical reasons, this one is called J/ψ particle); Ψ" is a second excitation, and so on. That is, names in the same cell are synonymous.

Some of the states are predicted, but have not been identified; others are unconfirmed. Particle X(3872) quantum numbers are unknown; its identity is dabated. It may be:

• a candidate for the 1³D₂ state;
• a charmonium hybrid state;
• a molecule.

Term symbol	IG(JPC)	Particle	mass (MeV)
11S0	0+(0−+)	ηc (1S), or ηc(2980)	2979.6±1.2
13S1	0−(1−−)	J/ψ(1S)	3096.916±0.011
11P1	0−(1+−)	hc (1P)	3526.2*
13P0	0+(0++)	χc0 (1P)	3415.2
13P1	0+(1++)	χc1(1P)	3510.5
13P2	0+(2++)	χc2(1P)	3556.3
21S0	0+(0−+)	ηc(2S), or	3654*
23S1	0−(1−−)	ψ(3686)	3686.093±0.034
11D2	0+(2−+)	ηc2(1D)‡
13D1	0−(1−−)	ψ(3770)	3770.0±2.4
13D2	0−(2−−)	ψ(3836)•	3836±13
13D3	0−(3−−)	ψ3(1D)‡
21P1	0−(1+−)	hc(2P)‡
23P0	0+(0++)	χc0(2P)‡
23P1	0+(1++)	χc1(2P)‡
23P2	0+(2++)	χc2(2P)‡
????	0?(??)†	X(3872)	3872.0

Notes:

^* Needs confirmation.

^‡ Predicted, but not yet identified.

^• Candidate. Confirmation needed.

^† Interpretation as a 1⁻⁻ charmonium state not favored.

External links

• cc-bar messons