Diquark

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In quark-diquark models, a diquark, or diquark correlation/clustering, is the hypothetical state of two quarks grouped inside a baryon (that consists of three quarks)[1]. The diquark is often treated as a single 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 understand 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).


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[edit] Force between diquarks

The forces bewween the two quarks in a diquark is attractive when both the colours and spins are anitsymmetric. 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.


[edit] Controversy

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


[edit] 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.


[edit] 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 of hadrons that are created by fast-moving quarks. In the experiment the quarks ionized the vacuum area. This produced the quark–antiquark pairs, the Quark-Antiquark pairs 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 u,d,s quarks. Scientists found that the Λ contains the [ud] diquark, however the Σ does not. From this experiment scientists inferred that Λ baryons are more common than Σ baryons. They are indeed more common. (by a factor of 10)

[edit] References and additional reading

  • [1] Lichtenberg DB, Namgung W, Predazzi E, Wills JG, Baryon Masses In A Relativistic Quark-Diquark Model, Physical Review Letters 48 (24): 1653-1656 1982
  • Rapp R, Schafer T, Shuryak E, et al. Diquark bose condensates in high density matter and instantons Physical Review Letters 81 (1): 53-56 JUL 6 1998