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In quantum chromodynamics (QCD), today's accepted theory for the description of the strong nuclear force, gluons are exchanged when particles with a color charge interact. When two quarks exchange a gluon, their color charges change; the gluon carries an anti-color charge to compensate for the quark's old color charge, as well as the quark's new color charge. Since gluons thus carry a color charge themselves, they can also interact with other gluons, which makes the mathematical analysis of the strong nuclear force quite complicated and difficult.

The first experimental traces of gluons were found in the early 1980s at the large electron-positron collider PETRA at the DESYThe DESY Deutsches Elektronen Synchrotron "German Electron Synchrotron") is a major European center for particle physics and synchrotron radiation research and is member of and mostly financed by the Helmholtz Association of National Research Centres. in HamburgHamburg is Germany's second largest city (after Berlin) and its principal port. The official name Freie und Hansestadt Hamburg recalls its membership in the mediaeval Hanseatic League and the fact that Hamburg is a city state and one of Germany's sixteen, when evidence for a clear three-jet structure was found; the third jet was attributed to one of the produced quarks emitting a gluon.

Why are there only 8 gluons?

From a layman's point of view, there theoretically are nine unique color combinations for gluons, one for each combination of color (red, green and blue) and anti-color: .

In mathematical terms, however, there actually exists an infinite number of gluons, each of them being a normalised linear superposition of the ones listed above (for example, etc). Furthermore, since experiments show that colorless baryonIn particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called nucleons), as well as a number of unstable, heavier particles (called hyperons). The term "baryon" is derived from the Greek bars do not interact, the following property must hold; if it did not, baryons would be able to emit these gluons to interact with each other via the strong force.

No other linearly independent relation exists between gluons; thus, there are only eight linearly independent gluons, a statement that is typically simplified to "there are only 8 gluons". For a more detailed explanation involving SU(3)In mathematics, the special unitary group of degree n is the group of n by n unitary matrices with determinant 1 and entries from the field C of complex numbers, with the group operation that of matrix multiplication. It is written as SU n . This is a sub symmetry, see [1].