<div dir="ltr"><div>Ok here is the final version after some comment from Ole :<br><br>The Generalized Parton <br>Distributions (GPDs) are a more general formalism <br>encompassing the concept of elastic form factor (FF) and parton <br>
distributions (PDFs) introducing a third independent variable called <br>skewdness xi in addition to usual x\textunderscore bj and t variables which <br>are defined for the PDFs. Those distributions thus contain more information <br>
than the FF and PDFs allowing to give a more spatial and dynamical <br>description of the nucleon. To measure GPDs one has to measure exclusive <br>reaction. The simplest exclusive reaction is the exclusive production of <br>
photons or Deeply Virtual Compton Scattering. One drawback of this <br>measurement is that the real photon constrains the measurement of the GPDs <br>to the line xi$=$x. The Doubly Virtual Compton Scattering (DDVCS) is the <br>
similar process involving a virtual photon in the final state. This virtual <br>photon decays into a dilepton pair allowing some values of xi different than <br>x\textunderscore bj. High luminosity is required since cross sections are <br>
smaller by a factor 100. I will present how the SuperBigBite spectrometer <br>could be used to measure the DDVCS process particularly in the dimuon <br>channel.<br><br></div>Alexandre<br></div><div class="gmail_extra"><br>
<br><div class="gmail_quote">On Mon, Jul 1, 2013 at 10:15 AM, Alexandre Camsonne <<a href="mailto:camsonne@jlab.org">camsonne@jlab.org</a>> wrote:<br><blockquote class="gmail_quote">
<div dir="ltr"><div><div>Hello, <br><br></div>here is the abstract for Double DVCS. I might remove it if I figure out the acceptance is not large enough to make an interesting measurement.<br><br>Alexandre Camsonne for the Hall A SuperBigBite Collaboration<br>
<br>Double Deeply Virtual Compton Scattering in Hall A using SuperBigBite Spectrometer<br> <br>The Generalized Parton Distributions (GPDs) are a more general formalism englobing the concept of elastic form factor (FF) and parton distributions (PDFs) introducing a third independent variable called skewdness xi in addition to usual x_bj and t variables which are define for the PDFs. Those distributions thus contain more informations than the FF and PDFs allowing to give a more spatial and dynamical description of the nucleon. To measure GPDs one has to measure exclusive reaction. The simpliest exclusive reaction is the exclusive production of photons or Deeply Virtual Compton Scattering. One drawback of this measurement is that the real photon constrains the measurement of the GPDs to the line xi=x. The Doubly Virtual Compton Scattering (DDVCS) is the similar process involving a virtual photon in the final state. This virtual photon decays into a dilepton pair allowing some values of xi different than x_bj. High luminosity is required since cross sections are smaller by a factor 100. I will present an idea using the SuperBigBite Spectrometer to try to measure the DDVCS particularly in the dimuon channel.<font color="#888888"><br>
<br></font></div><font color="#888888">Alexandre<br><div><br></div></font></div>
</blockquote></div><br></div>