Glueball

Glueball or Gluonenball also Gluonium , referred to in the particle , a hypothetical subatomic particle consisting only of Gluons (and sea quarks exists). Glueballs have not yet been detected.

Basics

Gluons mediate the strong interaction and thereby couple to the color charge of elementary particles . This is analogous to electromagnetic interaction , in which photons couple to the electrical charge . A major difference is that gluons themselves carry color charges and thus - in contrast to photons - can interact directly with one another. Hence there could be particles that are only composed of gluons.

properties

2-gluon systems
L.	S.	J ^PC
0	0, 2	0 ⁺⁺ , 2 ⁺⁺
1	1	0 ^{- +} , 1 ^{- +} , 2 ^{- +}
2	0, 2	0 ⁺⁺ , 2 ⁺⁺ , 4 ⁺⁺
3	1	2 ^{- +} , 3 ^{- +} , 4 ^{- +}

Since gluons have integer spin (s = 1), no electrical charge and no flavors , this should also apply to glueballs. You would be uncharged mesons with no flavor.

In the case of gluon balls made of two gluons, their spins couple to S = 0, 1 or 2. For reasons of symmetry, S can only have the values 0 and 2 with an even orbital angular momentum L, and only the value 1 with an uneven orbital angular momentum. It is unusual here that mesons with a total spin J = 2 already appeared in the ground state (L = 0) .

With gluon balls made up of three or more gluons, the situation is more complicated.

proof

So far Glueballs could not be proven beyond doubt. The search is made more difficult by the fact that quantum mechanical mixtures of glueballs and “classical” mesons with the same quantum numbers are possible.

Candidates for Glueballs could be:

Mesons with "exotic" quantum numbers that are not possible for quark - antiquark states, e.g. B. J ^PC = 1 ^{- +} and J ^PC = 3 ^{- +}
“Redundant” mesons that do not fit into the known multiplets .

Individual evidence

↑ FEClose , PRPage: Gluon balls - structures made of pure nuclear power . In: Spectrum of Science . Jan, 1999, p. 48 .
^ Walter Taki: Search for Glueballs. (PDF) 1996, accessed on September 2, 2014 (English).

[Close-1] FEClose , PRPage: Gluon balls - structures made of pure nuclear power . In: Spectrum of Science . Jan, 1999, p. 48 .

[Taki-2] Walter Taki: Search for Glueballs. (PDF) 1996, accessed on September 2, 2014 (English).