last update : 01-15-07

  This page is a summary of the research I did for my Phd.

Virtual Compton Scattering  (VCS) of the proton below pion threshold :

The scattering of a photon off a proton allows the measurement of the rigidity of the internal structure of the nucleon. It is a fundamental process as the shape of the proton (as measured with the nucleon form factors) is modified under the influence of the scattered photon. Below pion production threshold (but arbitrary squared quadri-momentum transfer of the virtual photon), the measured observables are the Generalized Polarizabilities (GP). They generalize the concept of electric and magnetic polarizabilities measured in Real Compton Scattering. Between 1995 and 1998 we have measured the absolute unpolarized cross-sections for the photon electro-production off the Proton with the three-Spectrometer-Setup at MAMI  (Mainz, Germany) at a momentum transfer of 0.33 GeV2/c2   and a virtual photon polarization of 0.62. We extracted two combinations of the generalized polarizabilities and compared them to theoretical predictions of the non perturbative structure of the nucleon. Our experiment at Mainz was the first precise measurement of the photon electro production to be carried on, thanks to the advance of the CW beam delivery technology. Since that time, similar experiments have been performed at JLab/Hall A and MIT/Bates. The advance of the theoretical formalism allows also to measure the GP in the Delta region where the effect is larger.