| Quark Confinement |
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The reasons for quark confinement are somewhat complicated; there is no analytic proof that Quantum Chromodynamics should be confining, but intuitively confinement is due to the force-carrying Gluon s having colour charge. As two Electrically-charged particles separate, the Electric Field s between them diminish quickly, allowing Electron s to become unbound from Nuclei . However, as two quarks separate, the gluon fields form narrow Tubes (or strings) of colour charge. Thus the force experienced by the quark remains constant regardless of its distance from the other quark. Since energy goes as force times distance, the total energy increases linearly with distance. When two quarks become separated, as happens in Particle Accelerator collisions, at some point it is more energetically favorable for a new quark/anti-quark pair to "pop" out of the Vacuum than to allow the quarks to separate further. As a result of this, when quarks are produced in particle accelerators, instead of seeing the individual quarks in detectors, scientists see "jets" of many colour-neutral particles ( Meson s and Baryon s), clustered together. This process is called Hadronization , fragmentation or string breaking, and is one of the least understood processes in particle physics. The confining phase is usually defined by the behavior of the 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 will be 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 in the opposite direction will have only a small area between the two loops. Besides QCD in 4D, another model which exhibits confinement is the Schwinger Model . Compact Abelian gauge theories also exhibit confinement in 2 and 3 spacetime dimensions. SEE ALSO
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