Nuclear Physics Division

Deeply Virtual Compton Scattering (DVCS) is the simplest hard exclusive process related to Generalized Parton Distributions (GPDs): the scattering of an electron off a proton through the exchange of a photon of virtuality Q², accompanied by the re-emission of a real photon.

At large Q² and low transfer t the GPD formalism may be applied. In particular the beam helicity asymmetry of the electroproduction of a real photon is proportional (at first order in perturbative QCD) to the imaginary part of the DVCS amplitude. 

GPDs are supposed to deliver a more complete information on the interactions between quarks and gluons to form the  nucleons (and all the hadrons): three-dimensional imaging, quark angular momentum... Factorisation theorems relate GPDs to the observables of the photon  (DVCS) and meson production induced by lepton beams (electrons and muons).

The planned experiments have the goal to determine the validity domain of these theorems and to bring experimental constraints to these distributions.
 
CLAS Collaboration

Construction of a magnet, a magnetic calorimeter and a tracker to upgrade the CLAS detector (Cebaf Large Acceptance Spectrometer in the Hall B at Jefferson Lab) to allow the detection of photons at very small angles (with respect to the beam direction).

COMPASS Collaboration

Construction  and installation at COMPASS, CERN, of the detector CAMERA to detect the recoil proton in  the DVCS reaction, allowing to explore the spatial distribution of the nucleon components.