Parton

A point-like constituent of a hadron in high-energy collision models, chiefly a quark or gluon. Partons explain how hadrons behave in energetic scattering.

Deep inelastic scattering: A lepton–hadron collision in which a lepton probes a hadron at short distances through a highly virtual exchanged particle. Its scattered leptons revealed point-like constituents inside protons.
Hadron: A composite particle bound by the strong interaction, such as a proton or neutron. Partons are the short-distance constituents used to describe hadron collisions.
Richard Feynman: An American theoretical physicist who introduced the parton model to describe high-energy hadron collisions. He named and developed the model that gives these constituents their term.
Hard scattering: A collision process involving a large momentum transfer that probes short-distance particle interactions. The parton model treats many energetic hadron collisions as hard scattering between constituents.
Constituent quark model: A low-energy model that treats hadrons as bound states of a small number of effective massive quarks. It describes hadron properties at low energies, unlike the high-energy parton picture.
Parton distribution function: A function describing the probability density for finding a parton carrying a fraction of a hadron’s momentum at a specified scale. It quantifies the momentum fractions carried by the partons that collide.
Quark: An elementary fermion that carries color charge and participates in the strong interaction. Quarks are one of the two principal kinds of parton.
James Bjorken: An American theoretical physicist whose scaling ideas helped interpret deep-inelastic electron–proton scattering. His scaling predictions connected experimental results to point-like proton constituents.
Hadron collider: A particle accelerator that collides beams of hadrons to study high-energy interactions. Its predictions depend on the distributions and interactions of incoming partons.
Quark model: A classification and structural model of hadrons in terms of their valence quarks. Its valence-quark account is simpler than the scale-dependent sea and gluon content in parton descriptions.

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