[Deeppwg] abstract DIS 2011 for He-DVCS

[GUIDAL Michel (57321)]

Dear colleagues,

Yohann Perrin (from Grenoble) wishes to submit the following abstract for 
DIS'11. Please, send remarks, if any, to Eric Voutier (voutier at jlab.org)
AND Yohann Perrin (perrin at jlab.org). The abstract submission deadline is 
thursday evening, please send comments before then,
Amities,

Michel

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Title : Coherent deeply virtual Compton scattering off helium
Presenter : Y. Perrin (LPSC Grenoble) for the CLAS Collaboration

Since the observation by the European Muon Collaboration of the impact of the 
nuclear environnement
on the internal structure of the nucleon, the partonic structure of nuclei has 
been a great deal of interest.
A novel way to address this problem has emerged with the advent of the 
Generalized Parton Distribution
(GPD) framework which encodes the partonic structure of the nuclei and leads to 
a universal description
of many features of the nuclear structure (form factors, patron distributions, 
nucleon spin...). Because of
its density and spin, the helium nucleus is a privileged target for this study.

Deeply virtual Compton scattering (DVCS) yields the easiest access to GPDs via 
the Compton form factors.
This reaction consists of the coherent interaction of the electron with a 
parton of the nucleus, producing
a photon in the final state : e + He -->  e + He + gamma. By measuring the beam 
spin asymmetry it is
  possible to access the real and imaginary parts of the Compton form factor, 
thanks to the spin zero of
the helium nucleus.

The eg6 experiment at the Jefferson Lab probed the helium nucleus using the 6 
GeV polarized electron
beam of the Thomas Jefferson National Accelerator Facility (Newport News, VA). 
Data were collected
in the experimental Hall B using the CLAS detector complemented with an inner 
electromagnetic
calorimeter (for small angle photons measurement) and a radial time projection 
chamber (for helium
nuclei detection). This talk will review the eg6 experiment and present the 
current status of experimental
data.

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