Quarkonium
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In high energy physics, a quarkonium (pl. quarkonia) is a flavorless meson constituted by the association of a quark an its own antiquark, such as the charmonium or the bottomonium. Examples of quarkonia are the J/ψ (which is a charmonium state) and the Υ (a bottomonium state). Because of the high mass of the top quark, a toponium does not exist, since the quark decays through its electroweak interaction before the bound state can form. Mesons made in the same way with the light quarks are usually not called quarkonia. This is partly because they mix among themselves.
Because of the large seperation in masses between the charm, bottom and the remaining quarks, the charmonium and bottomonium families do not mix with each other, or with the other flavourless mesons.
| Contents |
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 debated. 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.
Bottomonium states
In the following table, the same particle can be named with the spectroscopic notation or with its mass.
Some of the states are predicted, but have not been identified; others are unconfirmed.
| Term symbol | IG(JPC) | Particle | mass (MeV) |
|---|---|---|---|
| 11S0 | 0+(0−+) | ηb(1S)* | 9300±20 |
| 13S1 | 0−(1−−) | Υ(1S) | 9460.3 |
| 11P1 | 0−(1+−) | hb(1P) | |
| 13P0 | 0+(0++) | χb0(1P) | 9859.0±1.0 |
| 13P1 | 0+(1++) | χb1(1P) | 9892.7 |
| 13P2 | 0+(2++) | χb2(1P) | 9912.6 |
| 21S0 | 0+(0−+) | ηb(2S) | |
| 23S1 | 0−(1−−) | Υ(2S) | 10023.26 |
| 11D2 | 0+(2−+) | ηb2(1D) | |
| 13D1 | 0−(1−−) | Υ(1D) | |
| 13D2 | 0−(2−−) | Υ2(1D) | |
| 13D3 | 0−(3−−) | Υ3(1D) | |
| 21P1 | 0−(1+−) | hb(2P) | |
| 23P0 | 0+(0++) | χb0(2P) | 10 232.1 |
| 23P1 | 0+(1++) | χb1(2P) | 10 255.2 |
| 23P2 | 0+(2++) | χb2(2P) | 10 268.5 |
| 33S1 | 0−(1−−) | Υ(3S) | 10 355.2 |
| 43S1 | 0−(1−−) | Υ(4S) or Υ(10580) | 10 580.0 |
| 53S1 | 0−(1−−) | Υ(10860) | 10 865 |
| 63S1 | 0−(1−−) | Υ(11020) | 11 0219 |
Notes:
- * Preliminary results. Confirmation needed.
QCD and quarkonia
The computation of the properties of mesons in Quantum chromodynamics (QCD) is a fully non-perturbative one. As a result, the only general method available in a lattice QCD computation. However, there might be some simplification for the heavy quarkonia.
The light quarks in a meson move at relativistic speeds, since the mass of the bound state is much larger than the mass of the quark. However, the charm and the bottom quarks in their quarkonia move relatively slowly. It is estimated that the speed, v, is 0.3 times the speed of light for charm and 0.1 times the speed of light for bottom. It is then possible to approximate the computation as an expansion in powers of v. This is called non-relativistic QCD (NRQCD).
NRQCD has also been quantized as a lattice gauge theory. This makes the computation of quarkonium properties somewhat simpler. Good agreement with the bottomonium masses has been found. Indeed this provides one of the best controlled non-perturbative tests of QCD. For the charm family the agreement is not as good. Presumably v is not small enough for NRQCD to be accurate.
Disappearance of quarkonia has been suggested as a diagnostic of the formation of the quark-gluon plasma in experiments.
See also
|
Particles in Physics - Composite particles | Edit (http://en.wikipedia.org/w/wiki.phtml?title=Template:Composite&action=edit) |
| Molecules | Atoms | Atomic nuclei | Hadrons | Baryons | Mesons | Exotic baryons | Exotic mesons | Tetraquarks | Pentaquarks | Hyperons | Hybrids |
