Editing Color confinement (section)

==Origin ==
There is not yet an analytic proof of color confinement in any [[non-abelian gauge theory]].  The phenomenon can be understood qualitatively by noting that the force-carrying [[gluon]]s of QCD have color charge, unlike the photons of [[quantum electrodynamics]] (QED).  Whereas the [[electric field]] between [[electric charge|electrically charged]] particles decreases rapidly as those particles are separated, the [[gluon field]] between a pair of color charges forms a narrow flux tube (or string) between them.  Because of this behavior of the gluon field, the strong force between the particles is constant regardless of their separation.<ref>
{{Cite book
 |last=Muta |first=T.
 |year=2009
 |title=Foundations of Quantum Chromodynamics: An introduction to perturbative methods in gauge theories
 |url=https://books.google.com/books?isbn=9812793534  
 |edition=3rd
 |volume=78
 |series=[[Lecture Notes in Physics]]
 |publisher=[[World Scientific]]
 |isbn=978-981-279-353-9
}}</ref><ref>
{{Cite book
 |last=Smilga |first=A.
 |year=2001
 |title=Lectures on quantum chromodynamics
 |url=https://books.google.com/books?isbn=9810243316  
 |publisher=[[World Scientific]]
 |isbn=978-981-02-4331-9
}}</ref>

Therefore, as two color charges are separated, at some point it becomes energetically favorable for a new quark–antiquark [[pair production|pair]] to appear, rather than extending the tube further. As a result of this, when quarks are produced in particle accelerators, instead of seeing the individual quarks in detectors, scientists see "[[jet (particle physics)|jets]]" of many color-neutral particles ([[meson]]s and [[baryon]]s), clustered together. This process is called ''[[hadronization]]'', ''fragmentation'', or ''string breaking''.

The confining phase is usually defined by the behavior of the [[action (physics)|action]] of the [[Wilson loop]], which is simply the path in [[spacetime]] traced out by a quark–antiquark pair created at one point and annihilated at another point. In a non-confining theory, the action of such a loop is proportional to its perimeter. However, in a confining theory, the action of the loop is instead proportional to its area. Since the area is proportional to the separation of the quark–antiquark pair, free quarks are suppressed. Mesons are allowed in such a picture, since a loop containing another loop with the opposite orientation has only a small area between the two loops. At non-zero temperatures, the [[order operator]] for confinement are thermal versions of Wilson loops known as [[Polyakov loop]]s.