A constituent quark is a
current quark with a notional "covering" induced by the
renormalization group
In theoretical physics, the renormalization group (RG) is a formal apparatus that allows systematic investigation of the changes of a physical system as viewed at different scales. In particle physics, it reflects the changes in the underlying p ...
.
In the low-energy limit of
QCD, a description by means of
perturbation theory
In mathematics and applied mathematics, perturbation theory comprises methods for finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem. A critical feature of the technique is a middle ...
is not possible: Here, no
asymptotic freedom exists, but collective
interactions between
valence quark
In particle physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks that give rise to the quantum numbers of the hadrons. The quark model underlies Flavour (particle physics), ...
s and
sea quarks gain strongly in significance. Part of the effects of
virtual quarks and virtual gluons in the "sea" can be assigned to a
quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...
so well that the term "constituent quark" can serve as an effective description of the low-energy system.
Constituent quarks appear like "dressed" current quarks, i.e. current quarks surrounded by a cloud of virtual quarks and gluons. This cloud, in the end, underlies the large constituent-quark masses.
;Definition: Constituent quarks are valence quarks for which the correlations for the description of hadrons by means of gluons and sea-quarks are put into effective quark masses of these valence quarks.
The effective quark mass is called constituent quark mass. Hadrons consist of "glued" constituent quarks.
Binding energy
The
quantum chromodynamic binding energy of a valence quark in a hadron is the amount of energy required to make the hadron spontaneously emit a meson containing the valence quark. This is the same as the constituent-quark mass.
Note that the following values are model-dependent.
References
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Quarks