Helicity dependence of the reaction channels above π-threshold

Based on a prior effective Lagrangian model on single pion photoproduction from the nucleon, successfully tested in total and differential cross-sections, we study theoretically the helicity dependence from the interaction of circularly polarized photons and a longitudinally polarized nucleon target in the energy range from π-threshold through the Δ(1232)-resonance region. The doubly polarized total and differential cross-section differences for parallel and antiparallel helicity states are predicted and compared with the experiment. We show that the results are sensitive to interferences among different contributions to the process and, thus, represent a complementary test of the theoretical model. A quite satisfactory agreement with recent experimental data from the GDH-collaboration is obtained.