Gluon

In physics, gluons are the elementary particles which are responsible for the strong nuclear force. They bind quarks together to form protons and neutrons as well as other hadrons; their electric charge is zero, their spin is 1 and they are generally assumed to have zero mass. Gluons are ultimately responsible for the stability of atomic nuclei.

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. Even though there are theoretically nine unique colour combinations for gluons, (r-ar, r-ag, r-ab, g-ar, g-ag, g-ab, b-ar, b-ag, and b-ab) in reality there are only eight.

The first experimental traces of gluons were found in the early 1980s at the electron-positron-collider PETRA at the DESY in Hamburg, when evidence for a clear three-jet structure was found; the third jet was attributed to one of the produced quarks emitting a gluon.