First Determination of Generalized Polarizabilities of the Proton by a Virtual Compton Scattering Experiment

Abstract

Absolute differential cross sections for the reaction $\mathrm{ep}\ensuremath{\rightarrow}\mathrm{ep}\ensuremath{\gamma}$ have been measured at a four-momentum transfer with virtuality ${Q}^{2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.33{\mathrm{GeV}}^{2}$ and polarization $\ensuremath{\epsilon}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.62$ in the range 33.6 to $111.5\mathrm{MeV}/c$ for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high-resolution spectrometers at the Mainz Microtron MAMI. From the photon angular distributions, two structure functions which are a linear combination of the generalized polarizabilities have been determined for the first time.