Strange Baryons Beyond Protons and Neutrons
Hyperons are a class of baryons that contain one or more strange quarks. They are heavier than nucleons (protons and neutrons) and play an important role in understanding the strong interaction and strangeness quantum number.
Hyperons were discovered in cosmic ray experiments during the 1940s and 1950s. Their unusually long lifetimes led to the concept of strangeness, which is conserved in strong interactions but violated in weak decays.
Hyperons are composed of three quarks, at least one of which is a strange quark (\(s\)).
| Hyperon | Symbol | Quark Content |
|---|---|---|
| Lambda | Λ⁰ | uds |
| Sigma | Σ⁺, Σ⁰, Σ⁻ | uus, uds, dds |
| Xi | Ξ⁰, Ξ⁻ | uss, dss |
| Omega | Ω⁻ | sss |
All hyperons have baryon number \(B = 1\).
The defining feature of hyperons is their non-zero strangeness:
\[ S = -n_s \]where \(n_s\) is the number of strange quarks.
Hyperons are fermions and therefore have half-integer spin:
\[ J = \frac{1}{2},\ \frac{3}{2} \]Hyperons are more massive than nucleons and are generally unstable. They decay via the weak interaction with lifetimes of the order \(10^{-10}\) seconds.
A typical weak decay of a hyperon is:
\[ \Lambda^0 \rightarrow p + \pi^- \]Such decays violate strangeness conservation but conserve charge, energy, and baryon number.