Constituent quark

A constituent quark is a current quark with a covering.

In the low energy limit of QCD, a description by means of perturbation theory is not possible. Here, no Asymptotic freedom exists, but the interactions between valence quarks and sea quarks gain strongly on significance. Part of the effects of virtual quarks and virtual gluons in the 'sea' can be assigned to a quark so well that the term 'constituent quark' seems appropriate.

According to the Feynman diagrams, constituent quarks seem to be 'dressed' current quarks, i.e. current quarks surrounded by a cloud of virtual quarks and gluons. This cloud in the end explains 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. The use of positions for the light constituent quarks is not exactly unproblematic in the description of hadrons.

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.

Constituent quark	Mass	Δx
Up quark	336 MeV/c^2[1]	0.7 fm
Down quark	340 MeV/c^2[1]	0.7 fm
Strange quark	486 MeV/c^2[1]
Charm quark	1550 MeV/c^2[1]
Bottom quark	4730 MeV/c^2[1]
Top quark	177000 MeV/c^2[1]

Describing hadrons using non-relativistic quantum mechanics becomes difficult.

References

1. Griffiths, David (2008). Introduction to Elementary Particles. WILEY-VCH. p. 135.