Current quarks, also known as naked or bare quarks, are the core valence quarks that form the invariable parts of a hadron, stripped of their surrounding gluons and virtual quarks. In quantum chromodynamics, the current quark mass refers to the mass of these real quarks, which is much smaller than the mass of the composite particle influenced by their gluon and virtual-quark “dressing.” Heavier quarks have masses that dominate over this covering, while lighter quarks have masses so small that their precise values are difficult to determine. By contrast, the constituent quark includes both the current quark and its surrounding dressing, with light quarks’ constituent masses roughly one-third of the average proton and neutron masses, plus some adjustment for the strange quark.
Abstraction vs. reality
Since it is not physically possible even at solar-interior temperatures to "strip naked" any quark of its covering, it is a matter of legitimate doubt whether current quarks are actual or real, or merely a convenient but unrealistic and abstract notion. High energy particle accelerators provide a demonstration that the idea of a "naked quark" is in some sense real: If the current quark imbedded in one constituent quark is hit inside its covering with large momentum, the current quark accelerates through its evanescent covering and leaves it behind, at least temporarily producing a "naked" or undressed quark, showing that to some extent the idea is realistic (see glueball for speculations about what happens to the dressing of virtual particles that gets left behind).
In addition, current quarks possess one asymptotic freedom within the limits described by perturbation theory.
The local term plays no more role for the description of the hadrons with the light current quarks. In the MS-scheme, at μ = 2 GeV/c2 , the quark masses are:5
| Current quark | Mass | Δx |
|---|---|---|
| Up quark (u) | 1.8~2.8 MeV/c2 | 20–40 fm |
| Down quark (d) | 4.3~5.2 MeV/c2 | 20–40 fm |
| Strange quark (s) | 92~104 MeV/c2 | |
| Charm quark (c) | 1.3 GeV/c2 | |
| Bottom quark (b) | 4.2~4.7 GeV/c2 | |
| Top quark (t) | 156~176 GeV/c2 |
For the lighter quarks6 a description with any accuracy is only possible with the help of relativistic quantum mechanics.
Current quark mass
The current quark mass is also called the mass of the 'naked' quarks. The mass of the current quark is reduced by the term of the constituent quark covering mass.
The current quark mass is a logical consequence of the mathematical formalism of the quantum field theory (QFT), so the idea does not arise from a strictly descriptive report of observations. The current quark masses of the light current quarks7 are much smaller than the constituent quark masses. Reason for this is the missing of the mass of the constituent quark covering.
The current quark mass is a parameter to compute sufficiently small color charges.
Definition The current quark mass means the mass of the constituent quark with the mass of the respective constituent quark covering subtracted away.There is almost no difference between current quark mass and constituent quark mass for the heavy quarks;8 this is not at all the case for the light quarks.9
The comparison of the results of the computations with the experimental data supplies the values for the current quark masses.
Footnotes
References
Smith, Timothy Paul (2003). Hidden Worlds: Hunting for quarks in ordinary matter. Princeton University Press. pp. 150–151. ISBN 978-0-691-05773-6. 978-0-691-05773-6 ↩
The so-called "heavy" quarks are the top (t), bottom (b), and charm (c) quarks. Their "naked" masses are all about 80% their "dressed" masses. /wiki/Top_quark ↩
The so-called "light" quarks are the up (u), down (d), and strange (s) quarks. Their "dressed" masses are all around 0.33~0.50 GeV, much larger than their "naked" masses, which tend to be around 0.05~0.20 GeV about 1 /5~1/ 20 th their "dressed" size. /wiki/Up_quark ↩
The so-called "light" quarks are the up (u), down (d), and strange (s) quarks. Their "dressed" masses are all around 0.33~0.50 GeV, much larger than their "naked" masses, which tend to be around 0.05~0.20 GeV about 1 /5~1/ 20 th their "dressed" size. /wiki/Up_quark ↩
Patrignani, C.; et al. (Particle Data Group) (2016). "Quarks" (PDF). Chin. Phys. C. 40: 100001 – via Lawrence Berkeley Laboratory. http://pdg.lbl.gov/2016/mobile/summary-tables/pdf/rpp2016-sum-quarks-m.pdf ↩
The so-called "light" quarks are the up (u), down (d), and strange (s) quarks. Their "dressed" masses are all around 0.33~0.50 GeV, much larger than their "naked" masses, which tend to be around 0.05~0.20 GeV about 1 /5~1/ 20 th their "dressed" size. /wiki/Up_quark ↩
The so-called "light" quarks are the up (u), down (d), and strange (s) quarks. Their "dressed" masses are all around 0.33~0.50 GeV, much larger than their "naked" masses, which tend to be around 0.05~0.20 GeV about 1 /5~1/ 20 th their "dressed" size. /wiki/Up_quark ↩
The so-called "heavy" quarks are the top (t), bottom (b), and charm (c) quarks. Their "naked" masses are all about 80% their "dressed" masses. /wiki/Top_quark ↩
The so-called "light" quarks are the up (u), down (d), and strange (s) quarks. Their "dressed" masses are all around 0.33~0.50 GeV, much larger than their "naked" masses, which tend to be around 0.05~0.20 GeV about 1 /5~1/ 20 th their "dressed" size. /wiki/Up_quark ↩