Hyperons

Hyperons are baryons that contain one or more strange quarks and no charm or heavier quarks. They are fermions with half-integer spin, and their masses are typically larger than those of nucleons because the strange quark is heavier. Hyperons carry nonzero strangeness and are usually produced in high-energy processes where strange quarks are created.

The lightest hyperons in the ground state include the Lambda zero (Λ0, quark content uds) and the Sigma triplet (Σ+, Σ0, Σ− with quark contents uus, uds, dds). Heavier strange baryons include the Xi (Ξ0, Ξ− with uss, dss) and the Omega minus (Ω− with sss). Many of these belong to the SU(3) flavor octet (spin-1/2) or decuplet (spin-3/2) multiplets, which organize baryons by quark content and quantum numbers.

Most hyperons decay via the weak interaction to lighter baryons and mesons, giving lifetimes on the order of 10−10 seconds. The Sigma0 is an exception: it decays electromagnetically to a Lambda and a photon with an extremely short effective lifetime, so it is not observed as a free particle. Hyperon production and decay properties provide tests of hadron structure, quark dynamics, and flavor symmetry.

Hyperons are observed in high-energy hadron collisions and in cosmic-ray interactions. Their study sheds light on strangeness production, hadronization processes, and nonperturbative aspects of quantum chromodynamics. In dense stellar environments, such as neutron stars, hyperons may appear at high densities and influence the equation of state of matter.