Helicity dependence of the γd → πNN reactions in theΔ -resonance region

The helicity dependence of the differential cross-section for the γd → πNN reactions has been measured for the first time in the Δ -resonance region. The measurement was performed with the large-acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. The data show that the main reaction mechanisms for the π ±NN channels are the quasi-free Nπ processes on one bound nucleon with nuclear dynamics playing a minor role. On the contrary, for the π 0 np channel nuclear mechanisms involving the reabsorption of the photoproduced π 0 by the np pair have to be taken into account to reproduce the experimental data.