# hyperon

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## hyperon

**hyperon**(hīˈpərŏnˌ), class of elementary particles heavier than nucleons (proton and neutron). The nucleons and the hyperons together make up the baryon family of particles.

## Hyperon

A collective name for any baryon with nonzero strangeness number *s*. The name hyperon has generally been limited to particles which are semistable, that is, which have long lifetimes relative to 10^{-22} s and which decay by photon emission or through weaker decay interactions. Hyperonic particles which are unstable (that is, with lifetimes shorter than 10^{-22} s) are commonly referred to as excited hyperons. The known hyperons with spin ^{1}/_{2} ℏ (where ℏ is Planck's constant divided by 2π) are Λ, Σ^{-}, Σ^{0}, and Σ^{+} with *s* = -1, and Ξ^{-} and Ξ^{0}, with *s* = -2, together with the Ω^{-} particle, which has spin ^{3}/_{2} ℏ and *s* = -3. The corresponding antihyperons have baryon number *B* = -1, opposite strangenesse *s*, and charge *Q*; they are all known empirically.

There is no deep distinction between hyperons and excited hyperons, beyond the phenomenological definition above. Indeed, the hyperon Ω(1672)^{-} and the excited hyperons Ξ(1530) and Σ(1385), together with the unstable nucleonic states Δ(1236), are known to form a unitary decuplet of states with spin ^{3}/_{2} ℏ. *See* Baryon, Elementary particle, Symmetry laws (physics), Unitary symmetry

## hyperon

[′hī·pə‚rän]*B*= + 1, that is, which can be transformed into a nucleon and some number of mesons or lighter particles, and which has nonzero strangeness number.

^{-22}second).