Electroproduction

Electroproduction is the production of particles in scattering processes initiated by electrons via the electromagnetic interaction. In such reactions an incoming electron exchanges a virtual photon with a target such as a proton, neutron, or nucleus, converting the available energy into additional final-state particles, typically mesons or excited baryons. It differs from photo-production, which uses real photons, and from hadroduction, which relies on hadronic probes.

The process is described in terms of the four-momentum transfer Q^2, the energy transfer, and the invariant momentum transfer t. The exchanged photon is virtual (Q^2 > 0), and the cross section factorizes into a part describing the electron–photon interaction and a hadronic part encoding the target response. Cross sections can be separated into longitudinal and transverse components by varying electron kinematics (Rosenbluth separation). Measurements depend on Q^2 and the energy and momentum transferred to the hadronic system, revealing information about internal structure and dynamics.

Experimentally, electroproduction is studied at electron accelerators and fixed targets, such as Jefferson Lab, DESY, and other facilities. Observables include differential cross sections and polarization asymmetries, which yield information on nucleon form factors, transition form factors to excited states (N*) and generalized parton distributions that encode the spatial and momentum structure of the nucleon. Theoretical descriptions combine quantum electrodynamics for the lepton side with quantum chromodynamics or effective hadronic models for the strong-interaction side.

Common channels include electroproduction of pions (π0, π±), eta mesons, and vector mesons (ρ, ω, φ) on nucleons and nuclei. Electroproduction provides access to resonance spectra and to the dynamics of confinement, complementing deep inelastic scattering by probing exclusive processes and hadron structure.