Semi-Exclusive Processes: New Probes of Hadron Structure

摘要

We define and study hard ''semi-exclusive'' processes of the form A + B {r_arrow} C + Y which are characterized by a large momentum transfer between the particles A and C and a large rapidity gap between the final state particle C and the inclusive system Y. Such reactions are in effect generalizations of deep inelastic lepton scattering, providing novel currents which probe specific quark distributions of the target B at fixed momentum fraction. We give explicit expressions for photo- and leptoproduction cross sections such as {gamma}p {r_arrow} {pi}Y in terms of parton distributions in the proton and the pion distribution amplitude. Semi-exclusive processes provide opportunities to study fundamental issues in QCD, including odderon exchange and color transparency, and suggest new ways to measure spin-dependent parton distributions.