Three-quark hadrons obeying Fermi–Dirac statistics
Baryons are a class of hadrons composed of three quarks bound together by the strong interaction. They are fermions and therefore obey Fermi–Dirac statistics. The most familiar baryons are the proton and the neutron, which together form atomic nuclei.
The study of baryons provides direct experimental evidence for the quark model and the underlying theory of quantum chromodynamics (QCD).
| Property | Description |
|---|---|
| Constituents | Three quarks (qqq) |
| Spin | Half-integer (1/2, 3/2) |
| Statistics | Fermi–Dirac statistics |
| Baryon Number | +1 |
| Interactions | Strong, electromagnetic, weak |
Baryons are classified based on their spin, isospin, and the presence of heavier quarks such as strange, charm, or bottom.
Nucleons are the lightest baryons and include the proton and the neutron. They form the building blocks of atomic nuclei.
| Baryon | Symbol | Charge | Quark Composition |
|---|---|---|---|
| Proton | p | +1 | uud |
| Neutron | n | 0 | udd |
Hyperons are baryons that contain one or more strange quarks. They are heavier and generally unstable compared to nucleons.
| Hyperon | Symbol | Strangeness | Quark Content |
|---|---|---|---|
| Lambda | Λ⁰ | −1 | uds |
| Sigma | Σ⁺, Σ⁰, Σ⁻ | −1 | uus, uds, dds |
| Xi | Ξ⁰, Ξ⁻ | −2 | uss, dss |
| Omega | Ω⁻ | −3 | sss |
Since baryons are fermions, their total wave function must be antisymmetric under the exchange of any two quarks. This requirement is satisfied by introducing an additional quantum number known as color.
The possible total spin values of baryons arise from the coupling of the three quark spins:
Thus, baryons can exist in spin-\( \frac{1}{2} \) or spin-\( \frac{3}{2} \) states.
Baryons constitute nearly all the observable matter in the universe. Understanding their structure and interactions is essential for nuclear physics, astrophysics, and cosmology.
Modern experiments in high-energy physics continue to explore excited baryon states and exotic baryons, deepening our understanding of QCD.
The baryon octet consists of eight spin-1/2 baryons described by SU(3) symmetry.
| Baryon | Quark Content |
|---|---|
| p | u u d |
| n | u d d |
| Λ⁰ | u d s |
| Σ⁺ | u u s |
| Σ⁰ | u d s |
| Σ⁻ | d d s |
| Ξ⁰ | u s s |
| Ξ⁻ | d s s |
The baryon decuplet consists of ten spin-3/2 baryons with symmetric quark wavefunctions.
| Baryon | Quark Content |
|---|---|
| Δ⁺⁺ | u u u |
| Δ⁺ | u u d |
| Δ⁰ | u d d |
| Δ⁻ | d d d |
| Σ*⁺ | u u s |
| Σ*⁰ | u d s |
| Σ*⁻ | d d s |
| Ξ*⁰ | u s s |
| Ξ*⁻ | d s s |
| Ω⁻ | s s s |
Baryons are three-quark fermionic particles that form the core of ordinary matter. Their properties validate the quark model, demonstrate color confinement, and provide a testing ground for strong interaction theories.