The parton model approximates a high-energy collision with a hadron as a short interaction with one constituent carrying a fraction of the hadron's longitudinal momentum. In electromagnetic deep inelastic scattering, the probe couples to charged quarks and antiquarks.
The short collision is treated using a parton-level scattering probability, averaged over parton distribution functions. In the simplest massless collinear limit, the Bjorken scaling variable identifies the struck constituent's momentum fraction, and dimensionless structure functions approximately depend on that variable alone. QCD scaling violation adds logarithmic resolution dependence through radiation and splitting. The model explains why a composite target can display a simple short-distance pattern without requiring its constituents to be permanently isolated classical particles.
New to topics? Read the docs here!