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As Confinement ( English for, inclusion ') is referred to in the particle physics of the phenomenon that particles with dye loading not occur isolated. So come quarks and gluons only bound states before and can basically not as free particles are measured.

A complete theoretical description of this experimental finding is still pending.

Experimental Findings

In nature and in experiments, only color-neutral objects, i.e. H. Mesons (quark-antiquark pairs) or baryons (three-quark states) can be observed. Quarks and gluons are only " confined " in these states and not free. Attempts to "separate" the quarks with high energies resulted in a spontaneous pairing of quarks and antiquarks. It is assumed that gluons can come together to form glueballs , which are measurable bond states without valence quarks .

In the context of quantum chromodynamics ( quantum field theory of strong interaction ), confinement is related to the color charge of quarks and gluons: color charges come in three types, and for each color charge there is an opposite anti-color charge. If a particle contains a total of one unit of a color charge and one unit of the corresponding anti-color charge, it is color-charge neutral. In the same way, a particle in which each of the three color charges (or each of the three anti-color charges) occurs in the same strength is color-charge neutral. In more general terms, confinement means: "Only color-neutral objects occur in nature." The non-existence of the (inevitably color-charged) free individual quarks, so-called current quarks , is thus a special case of this more general formulation. It also has the consequence that the strong interaction only has a very short range , since no colored charge is "visible" to the outside.

With computer simulations one can show that a potential develops between two static quarks (pair generation is suppressed), which increases linearly with the distance. The linear potential leads to a force that remains constant with increasing distance, in contrast to z. B. Gravitation and electromagnetism , the force of which decreases quadratically with increasing distance. This linear potential is explained by the fact that, due to the color charge, the gluons combine to form a strand, the energy of which increases with length. Separating one color-charged particle from the rest would therefore require extremely high energy. A separation of the quarks from the gluons is therefore only possible under certain conditions and for a very short time. In reality, of course, the energy does not grow to infinity. From a certain energy (i.e. a certain distance between the quarks), new quark-antiquark pairs can arise, which bind with the previous ones to form new colorless states. This effect is known as “string breaking”.

The exact mechanisms by which the strand is formed are related to the interaction of the gluons with one another and their interaction with vacuum fluctuations and are the subject of current research. There are different scenarios how this strand can form. A uniform picture has not yet established itself. A complete understanding of confinement requires the development of suitable methods to solve many-body problems within quantum chromodynamics .

A potential well is often referred to as quantum mechanical confinement ( localization ).

See also

Individual evidence

  1. ^ A b R. Alkofer and J. Greensite: Quark Confinement: The Hard Problem of Hadron Physics . In: Journal of Physics . G, no. 34 , 2007, doi : 10.1088 / 0954-3899 / 34/7 / S02 , arxiv : hep-ph / 0610365 .
  2. ^ Christof Gattringer and Christian B. Lang: Quantum chromodynamics on the lattice: an introductory presentation . 1st edition. Springer, 2009, ISBN 978-3-642-01849-7 .