Antiquark

An antiquark is the antiparticle of a quark. For each quark flavor there exists a corresponding antiquark: anti-up (ū), anti-down (d̄), anti-charm (c̄), anti-strange (s̄), anti-top (t̄), and anti-bottom (b̄). Antiquarks carry the same mass as their quark partners but opposite electric charge and opposite quantum numbers such as color charge in quantum chromodynamics. In particular, the up quark has charge +2/3e, while its antiquark has −2/3e; the down quark has −1/3e, while its antiquark has +1/3e; and so on for the other flavors.

In hadrons, quarks and antiquarks combine in specific ways. Mesons are formed from a quark and an antiquark (for example, a pion can be composed of an up quark and an anti-down antiquark). Antibaryons are built from three antiquarks (for example, the antiproton consists of two anti-up quarks and one anti-down quark). The corresponding baryons are formed from three quarks. Antiquarks carry baryon number of −1/3 each, so antibaryons have baryon number −1, while mesons have baryon number 0.

Antiquarks participate in the same fundamental interactions as quarks: strong, electromagnetic, and weak forces, with charges and color attributes opposite to their quark partners. In quantum chromodynamics, antiquarks carry anticolor charges. Free quarks or antiquarks are not observed due to confinement; antiquarks are observed only within hadrons or in high-energy processes that produce quark–antiquark pairs.

Antiquarks are denoted by a bar over the corresponding quark symbol (for example, ū, d̄). They play a central role in particle production, annihilation processes, and the study of CP violation and matter–antimatter asymmetry in high-energy physics.