Definition of a Baryon
A baryon is a composite subatomic particle composed of three quarks held together by the strong nuclear force. It is a member of the hadron family, which also includes mesons (quark-antiquark pairs). Baryons are foundational to the structure of matter, primarily known through protons and neutrons, which form atomic nuclei.
Quarks and the Strong Force
The constituent quarks within a baryon interact via the strong nuclear force, which is mediated by particles called gluons. This force is incredibly powerful at short distances, ensuring that quarks remain confined within hadrons and are never observed in isolation. Baryons always contain three quarks, obeying specific color charge rules to maintain a 'colorless' state.
Common Examples: Protons and Neutrons
The most common and stable baryons are the proton and the neutron. A proton consists of two 'up' quarks and one 'down' quark (uud), giving it a net positive electric charge. A neutron is made of one 'up' quark and two 'down' quarks (udd), resulting in a net neutral charge. These particles collectively form the bulk of visible matter in the universe.
Role in Matter and Particle Classification
Baryons are classified as fermions, meaning they have half-integer spin and obey the Pauli exclusion principle, which dictates that no two identical fermions can occupy the same quantum state simultaneously. This property is crucial for the stability and structure of atomic nuclei. In cosmology, 'baryonic matter' refers to all ordinary matter composed of these particles, distinguishing it from dark matter.