Baryon

A particle with spin 1/2 (or 3/2) which consists of three elementary particles known as quarks. Baryons are the nucleons (protons and neutrons) which form atomic nuclei and also very shortlived (<10^-10 second) hyperons such as sigma particles.

Several grand-unified theories predict that baryons are not ultimately stable but indeed decay. Present theory and experimentation demonstrate that if protons are in fact unstable, they decay with a halflife of at least ~10³⁴ years.

See also: Antibaryon, Hadrons, Quark.