Polarized Compton scattering from He-4 in the Delta region

Differential cross sections and beam asymmetries of Compton scattering from He-4 have been measured with linearly polarized photons in the energy range from 206 to 310 MeV . The quality of the results has the potential to provide strong constraints on the understanding of the reaction mechanism in the Delta resonance region. A phenomenological analysis of the experimental results has been performed fitting the data to a multipole expansion including dipole and quadrupole scatterings in the impulse approximation. Results indicate that quadrupole contributions should not be neglected to reproduce the general trend of the experimental results. Comparison with predictions from recent theoretical models shows that important discrepancies exist particularly at backward angles. The additional information carried by the incident photon spin increases the difficulty in achieving a comprehensive description of experimental data.