Deep inelastic scattering

Deep inelastic scattering is high-energy lepton–hadron scattering in which the lepton transfers enough energy and momentum to reveal the hadron’s internal partonic structure.

Four-momentum transfer: The difference between a particle’s initial and final four-momenta, commonly denoted by q. Its squared magnitude sets the resolution scale of the probe.
SLAC-MIT experiment: A series of electron–proton and electron–deuteron scattering experiments performed at SLAC in the late 1960s. Its unexpectedly pointlike scattering revealed constituents inside nucleons.
Parton model: A model that describes high-energy hadron collisions as interactions with approximately free, pointlike constituents called partons. It provides the intuitive constituent picture behind deep-inelastic scattering.
HERA: A particle collider at DESY that collided electrons or positrons with protons from 1992 to 2007. Its wide kinematic reach produced precise measurements of proton structure functions.
Elastic scattering: A collision in which the particles’ internal states remain unchanged and only their momenta change. Unlike deep-inelastic events, elastic events leave the target intact.
Bjorken x: A dimensionless variable equal to the struck parton’s momentum fraction in the high-energy, near-collinear limit. It organizes measurements by the momentum fraction sampled inside the hadron.
Mott scattering: The relativistic scattering of electrons from pointlike charged particles, including spin effects. It supplied a point-particle reference for interpreting electron–proton cross sections.
Quark: A spin-one-half elementary particle that carries color charge and participates in the strong interaction. Quarks are the charged constituents most directly sampled by electromagnetic lepton scattering.
Electron–ion collider: A planned U.S. facility designed to collide polarized electrons with polarized protons and nuclei. It is designed to study parton distributions and the spin and spatial structure of hadrons.
Quasielastic scattering: A reaction in which a probe scatters from a bound constituent as if it were free, while the residual system may be excited. It probes individual constituents but lacks the highly excited hadronic final states characteristic of deep inelasticity.

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