The first virtual compton scattering experiment at MAMI

Virtual Compton scattering, i.e. the exclusive reaction γ ∗p → γ′p′ with γ ∗ denoting a virtual photon, provides new insights on the internal structure of the proton. Below π 0 production threshold, this experiment measures the generalized polarizabilities of the proton as defined by Guichon et al [1], [2] and Drechsel et al [3]. These new electromagnetic observables, functions of Q 2, enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering ( Q 2=0) [4]. The first VCS experiment [5] of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for Q 2=0.33 GeV 2 and we present in this paper the preliminary results.