nLab quark

Idea

Quarks (Gell-Mann 64, Zweig 64) are one of the fundamental particles/matter fields in the standard model of particle physics. Quarks couple to the Yang-Mills theory given by QCD.

Quarks come in three generations of fermions:

flavors of fundamental fermions in the standard model of particle physics:
generation of fermions	1st generation	2nd generation	3d generation
quarks ($q$)
up-type	up quark ($u$)	charm quark ($c$)	top quark ($t$)
down-type	down quark ($d$)	strange quark ($s$)	bottom quark ($b$)
leptons
charged	electron	muon	tauon
neutral	electron neutrino	muon neutrino	tau neutrino
bound states:
mesons	light mesons: pion ($u d$) ρ-meson ($u d$) ω-meson ($u d$) f1-meson a1-meson	strange-mesons: ϕ-meson ($s \bar s$), kaon, K*-meson ($u s$, $d s$) eta-meson ($u u + d d + s s$) charmed heavy mesons: D-meson ($u c$, $d c$, $s c$) J/ψ-meson ($c \bar c$)	bottom heavy mesons: B-meson ($q b$) ϒ-meson ($b \bar b$)
baryons	nucleons: proton $(u u d)$ neutron $(u d d)$

At room-temperature quarks always form bound states to hadrons. This phenomenon of confinement is quantitatively well-reproduced by lattice QCD computations (see Fodor-Hoelbling 12) and qualitatively well reproduced by conceptual arguments such as the AdS/QCD correspondence, but a full analytic proof of confinement from a rigorous AQFT-like foundation of QCD remains open, see the mass gap problem.

However, at high temperature QCD goes through a deconfinement phase transition and enters another phase of matter known as the quark-gluon plasma. As the name suggests, here quarks and gluons are free.

Related concepts

• constituent quark

  • diquark

• colour charge, flavour (particle physics)

• quantum chromodynamics

• confinement

  • quark bag model, Cheshire cat principle

  • chiral perturbation theory

  • AdS/QCD

• quark-hadron duality

• quark-gluon plasma

• generation of fermions

• hadron

  • meson, baryon

  • pentaquark

• B meson

• squark

References

General

• Jiri Chyla, Quarks, partons and Quantum Chromodynamics, (spire:674163/), pdf)

• Jean-Marc Richard, An introduction to the quark model (arXiv:1205.4326, spire:1115489)

• Particle Data Group, Quark Model (pdf, web), Chapter 15 in: The Review of Particle Physics, Prog. Theor. Exp. Phys. 2020, 083C01 (2020) (doi:10.1093/ptep/ptaa104)

Textbooks:

• Francis Halzen, Alan Martin, Quarks and Leptons: An Introductory Course in Modern Particle Physics, Wiley 1984 (pdf, spire:205394)

• Howard Georgi, §15 in: Lie Algebras In Particle Physics, Westview Press (1999), CRC Press (2019) [doi:10.1201/9780429499210]

Quark masses in terms of chiral perturbation theory:

• Jürg Gasser, Heinrich Leutwyler, Quark masses, Physics Reports Volume 87, Issue 3, July 1982, Pages 77-169 (doi:10.1016/0370-1573(82)90035-7)

History

The quark model was proposed independently in 1964 by

• Murray Gell-Mann, A Schematic Model of Baryons and Mesons, Phys.Lett. 8 (1964) 214-215 (spire:11880, doi:10.1016/S0031-9163(64)92001-3)

• George Zweig, An SU(3) model for strong interaction symmetry and its breaking, version 1 is CERN preprint 8182/TH.401, Jan. 17, 1964, version 2 in Developments in the Quark Theory of Hadrons Volume 1. Edited by D. Lichtenberg and S. Rosen. Nonantum, Mass., Hadronic Press, 1980. pp. 22-101 (spire:4674)

Review of this history:

• George Zweig, Origins of the quark model, 1980 (pdf, pdf)

Ab-initio lattice computation

Due to confinement, before the quark-gluon plasma was seen in experiment it was a logical possibility that the quark-model of QCD is not actually correct. But more recend ab-initio computation in lattice QCD show that starting with the quark model, at least the light hadron bound states observes in experiment are reproduced by these ab-initio computations. This is discussed in the following references, see the good review Fodor-Hoelbling 12

• S. Durr, Z. Fodor, J. Frison, C. Hoelbling, R. Hoffmann, S.D. Katz, S. Krieg, T. Kurth, L. Lellouch, T. Lippert, K.K. Szabo, G. Vulvert,

  Ab-initio Determination of Light Hadron Masses,

  Science 322:1224-1227,2008 (arXiv:0906.3599)

• Zoltan Fodor, Christian Hoelbling, Light Hadron Masses from Lattice QCD, Rev. Mod. Phys. 84, 449, (arXiv:1203.4789)

• S. Aoki et. al. Review of lattice results concerning low-energy particle physics (arXiv:1607.00299)

See also

• Wikipedia, Quark