The Generalized Parton Distributions program at Jefferson Lab

TL;DR

This paper discusses the development and experimental investigation of Generalized Parton Distributions (GPDs) at Jefferson Lab, highlighting recent results, upcoming experiments, and future plans to explore nucleon structure.

Contribution

It presents new experimental results on DVCS at 4.2 GeV, details upcoming high-precision experiments at 6 GeV, and outlines future plans including the 12 GeV upgrade for comprehensive GPD studies.

Findings

Clean sine wave single spin asymmetry in DVCS

Accurate GPD measurements over wide kinematics range

Potential to constrain phenomenological models

Abstract

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 Q2 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 DeltaVCS where one produces a resonance in the final state. 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.