Baryons

Baryons are a class of hadrons in the standard model of particle physics. They are composite particles made of three quarks bound together by gluons and participate in the strong, electromagnetic, and weak interactions. Baryons carry a baryon number of +1 and are fermions with half-integer spin, unlike mesons, which are quark–antiquark pairs and carry zero baryon number.

In the quark model, a baryon is formed from three quarks arranged in a color-anticolor combination, consistent with color confinement. The lightest baryons are the proton and neutron, composed of up and down quarks (proton: uud, neutron: udd). Other light baryons include the Lambda (uds), the Sigma triplet (uus, uds, dss), the Xi doublets (uss, dss) and the Omega minus (sss). Baryons also occur in flavor multiplets: an octet of spin-1/2 baryons and a decuplet of spin-3/2 baryons such as the Delta family and the Omega−.

Anti-baryons are the antiparticles of baryons and consist of three antiquarks; they have baryon number −1 and are produced in high-energy collisions. They annihilate with baryons in detectors and in cosmic rays.

Properties such as mass arise from the sum of constituent quark masses and the strong interaction binding energy. Protons and neutrons have masses near 938–939 MeV, while many heavier baryons lie above 1 GeV. The proton is stable; most other baryons decay via the weak interaction with lifetimes ranging from fractions of a picosecond to seconds, depending on the species.

Significance: Baryons form the bulk of ordinary matter, including protons and neutrons in atomic nuclei. Their interactions and decays test quantum chromodynamics and the symmetries of the Standard Model.