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.
The antiproton and the antineutron are antibaryons.
Subjects: Nuclear and Particle Physics