Exploring the Micro-Structure of the Proton: from Form Factors to DVCS

For a long time people made the mistake of thinking the proton was understood. New experiments, ranging from form factors to deeply virtual Compton scattering, promise a new era of highly informative studies. Among the controversial topics of the future may be such basic features as the physical size of the proton, the role of quark orbital angular momentum, and the possibility of making "femto-photographic" images of hadronic micro-structure.Comment: 19 pages, 2 figures, presented by John Ralston at the Workshop on "Testing QCD through Spin Observables in Nuclear Targets", University of Virginia, Charlottesville, Virginia, April 18-2

Uncovering the Scaling Laws of Hard Exclusive Hadronic Processes in a Comprehensive Endpoint Model

We show that an endpoint overlap model can explain the scaling laws observed in exclusive hadronic reactions at large momentum transfer. The model assumes one of the valence quarks carries most of the hadron momentum. Hadron form factors and fixed angle scattering are related directly to the quark wave function, which can be directly extracted from experimental data. A universal linear endpoint behavior explains the proton electromagnetic form factor, proton-proton fixed angle scattering, and the t-dependence of proton-proton scattering at large s>>t. Endpoint constituent counting rules relate the number of quarks in a hadron to the power-law behavior. All proton reactions surveyed are consistent with three quarks participating. The model is applicable at laboratory energies and does not need assumptions of asymptotically-high energy regime. A rich phenomenology of lepton-hadron scattering and hadron-hadron scattering processes is found in remarkably simple relationships between diverse processes.Comment: 23 pages, 7 figure