antidiquark

An antidiquark is a hypothetical bound state consisting of two antiquarks. In quantum chromodynamics, quarks carry color charge and combine in ways that produce color-singlet hadrons. A diquark, a correlated pair of quarks, is often modeled together with an antidiquark, a correlated pair of antiquarks, so that their combined color charges can form a color-singlet state. In many diquark–antidiquark models, the diquark is treated as a color antitriplet and the antidiquark as a color triplet, allowing them to bind into a tetraquark.

The antidiquark concept is most closely associated with tetraquark models, in which a tetraquark is described as a bound state of a diquark and an antidiquark. This framework provides a way to organize the internal quantum numbers of certain exotic hadrons that do not fit neatly into traditional quark–antiquark meson or three-quark baryon classifications. In these models, the spin, flavor, and spatial correlations within the antidiquark (and within the diquark) influence the properties and decays of the resulting tetraquark.

Beyond bound-state models, antidiquarks also appear in phenomenological descriptions of hadronization and jet fragmentation, where diquark–antidiquark pair production can contribute to the formation of baryons and antibaryons. However, there is no direct experimental observation of a standalone antidiquark; its existence is inferred from the broader interpretation of certain exotic hadron candidates as diquark–antidiquark bound states.

See also: diquark, tetraquark, hadron spectroscopy, quantum chromodynamics.