The parton model is a conceptual framework used in high-energy physics to describe the internal structure of hadrons (such as protons and neutrons) in terms of more fundamental constituents called partons—which include quarks and gluons.
Key ideas of the parton model:
- It was introduced by Richard Feynman to interpret the results of deep inelastic scattering experiments, where high-energy electrons are fired at protons.
- In these collisions, the proton behaves like a collection of point-like particles (partons) that absorb the momentum from the incoming electron.
- Partons include valence quarks, sea quarks (quark-antiquark pairs that briefly pop in and out of existence), and gluons.
In the infinite momentum frame, where the hadron moves nearly at the speed of light, its partons appear to be free and non-interacting during the short time of the collision. This simplification makes it possible to analyze experimental data using perturbative QCD.
The parton model laid the foundation for our modern understanding of quark-gluon structure in hadrons and contributed to the development of quantum chromodynamics (QCD), the current theory of the strong interaction. It also explains why high-energy collisions reveal a rich internal structure within protons, even though they appear point-like at low energies.