Misplaced Pages

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (January 2013) (Learn how and when to remove this message)

In particle physics, a diquark, or diquark correlation/clustering, is a hypothetical state of two quarks grouped inside a baryon (that consists of three quarks) (Lichtenberg 1982). Corresponding models of baryons are referred to as quark–diquark models. The diquark is often treated as a single subatomic particle with which the third quark interacts via the strong interaction. The existence of diquarks inside the nucleons is a disputed issue, but it helps to explain some nucleon properties and to reproduce experimental data sensitive to the nucleon structure. Diquark–antidiquark pairs have also been advanced for anomalous particles such as the X(3872).

Formation

The forces between the two quarks in a diquark is attractive when both the colors and spins are antisymmetric. When both quarks are correlated in this way they tend to form a very low energy configuration. This low energy configuration has become known as a diquark.

Controversy

Many scientists theorize that a diquark should not be considered a particle. Even though they may contain two quarks they are not color neutral, and therefore cannot exist as isolated bound states. So instead they tend to float freely inside hadrons as composite entities; while free-floating they have a size of about 1 fm. This also happens to be the same size as the hadron itself.

Uses

Diquarks are the conceptual building blocks, and as such give scientists an ordering principle for the most important states in the hadronic spectrum. There are many different pieces of evidence that prove diquarks are fundamental in the structure of hadrons. One of the most compelling pieces of evidence comes from a recent study of baryons. In this study the baryon had one heavy and two light quarks. Since the heavy quark is inert, the scientists were able to discern the properties of the different quark configurations in the hadronic spectrum.

Λ and Σ baryon experiment

An experiment was conducted using diquarks in an attempt to study the Λ and Σ baryons that are produced in the creation of hadrons created by fast-moving quarks. In the experiment the quarks ionized the vacuum area. This produced the quark–antiquark pairs, which then converted themselves into mesons. When generating a baryon by assembling quarks, it is helpful if the quarks first form a stable two-quark state. The Λ and the Σ are created as a result of up, down and strange quarks. Scientists found that the Λ contains the diquark, however the Σ does not. From this experiment scientists inferred that Λ baryons are more common than Σ baryons, and indeed they are more common by a factor of 10.

References

1. Ali, Ahmed; Maiani, Luciano; Polosa, Antonio D. (2019). Multiquark Hadrons. Cambridge University Press. p. 152. ISBN 978-1-107-17158-9. Retrieved 23 June 2020.
2. Peloso, Marco (2008). Continuous Advances In Qcd 2008 - Proceedings Of The Conference. World Scientific. p. 63. ISBN 978-981-4468-76-3. Retrieved 23 June 2020.
3. Montagna, G.; Nicrosini, O.; Vercesi, V. (2007). IFAE 2006: Incontri di Fisica delle Alte Energie - Italian Meeting on High Energy Physics - Pavia, Italy, 19-21 April 2006. Springer Science & Business Media. p. 52. ISBN 978-88-470-0530-3. Retrieved 23 June 2020.

Further reading

• D. B. Lichtenberg; W. Namgung; E. Predazzi; J. G. Wills (1982). "Baryon Masses In A Relativistic Quark-Diquark Model". Physical Review Letters. 48 (24): 1653–1656. Bibcode:1982PhRvL..48.1653L. doi:10.1103/PhysRevLett.48.1653.
• R. Rapp; T. Schëfer; E. Shuryak; M. Velkovsky (1998). "Diquark bose condensates in high density matter and instantons". Physical Review Letters. 81 (1): 53–56. arXiv:hep-ph/9711396. Bibcode:1998PhRvL..81...53R. doi:10.1103/PhysRevLett.81.53. S2CID 89610959.

v t e Particles in physics
Elementary	Fermions Quarks Up (quark antiquark) Down (quark antiquark) Charm (quark antiquark) Strange (quark antiquark) Top (quark antiquark) Bottom (quark antiquark) Leptons Electron Positron Muon Antimuon Tau Antitau Neutrino Electron neutrino Electron antineutrino Muon neutrino Muon antineutrino Tau neutrino Tau antineutrino Bosons Gauge Photon Gluon W and Z bosons Scalar Higgs boson Ghost fields Faddeev–Popov ghosts Hypothetical Superpartners Gauginos Gluino Gravitino Photino Others Axino Chargino Higgsino Neutralino Sfermion (Stop squark) Others Axion Curvaton Dilaton Dual graviton Graviphoton Graviton Inflaton Leptoquark Magnetic monopole Majoron Majorana fermion Dark photon Preon Sterile neutrino Tachyon W′ and Z′ bosons X and Y bosons
Composite	Hadrons Baryons Nucleon Proton Antiproton Neutron Antineutron Delta baryon Lambda baryon Sigma baryon Xi baryon Omega baryon Mesons Pion Rho meson Eta and eta prime mesons Bottom eta meson Phi meson J/psi meson Omega meson Upsilon meson Kaon B meson D meson Quarkonium Exotic hadrons Tetraquark (Double-charm tetraquark) Pentaquark Others Atomic nuclei Atoms Exotic atoms Positronium Muonium Tauonium Onia Pionium Protonium Superatoms Molecules Hypothetical Baryons Hexaquark Heptaquark Skyrmion Mesons Glueball Theta meson T meson Others Mesonic molecule Pomeron Diquark R-hadron
Quasiparticles	Anyon Davydov soliton Dropleton Exciton Fracton Hole Magnon Phonon Plasmaron Plasmon Polariton Polaron Roton Trion
Lists	Baryons Mesons Particles Quasiparticles Timeline of particle discoveries
Related	History of subatomic physics timeline Standard Model mathematical formulation Subatomic particles Particles Antiparticles Nuclear physics Eightfold way Quark model Exotic matter Massless particle Relativistic particle Virtual particle Wave–particle duality Particle chauvinism
Physics portal

• Quarks