The Generalized Parton Distributions (GPD) have drawn a lot of interest
from the theoretical community since 1997, but also from the experimental
community and especially at Jefferson Lab. First, the results for Deeply
Virtual Compton Scattering (DVCS) at 4.2~GeV beam energy have recently been
extracted from CLAS data. The single spin asymmetry shows a remarkably
clean sine wave despite the rather low $Q^2$ achievable at this energy. Two
new dedicated DVCS experiments using 6~GeV beam will run in 2003 and 2004 in
Hall~A and Hall~B respectively. Both experiments will yield very accurate
results over a wide range of kinematics, and allow for the first time
a precise test of the factorization of the DVCS process. Assuming the Bjorken
regime is indeed reached, these experiments will allow the extraction of
linear combinations of GPD\'s and put strong constraints on the available
phenomenological models. Upon successful completion of both experiments, a
wider experimental program at 6~GeV can be envisioned, using for instance
Deuterium targets trying to nail down the neutron and deuteron GPD\'s. In
addition, resonances can be probed using $\\Delta$VCS where one produces
a resonance in the final state. In a way similar to DVCS, such a process
depends on Transition GPD\'s which describe in a unique way the structure of
resonances. Finally, the 12~GeV upgrade of Jefferson Lab extends
the available kinematical range, and will allow us to perform a complete, high
precision GPD program using various reactions among which, Deeply Virtual Meson
Electroproduction (DVMP) and DVCS. |
