Helicity dependence and contribution to the Gerasimov-Drell-Hearn sum rule of the γ d → π NN reaction channels in the energy region from threshold up to the (1232) resonance

Abstract

The helicity dependence of the γ d→π−pp, γ d→π+nn, and γ d→π0np reaction channels is studied for incident photon energies from threshold up to the (1232) resonance with inclusion of leading πNN effects. The doubly polarized total and differential cross sections for parallel and antiparallel helicity states are predicted. Then the contribution of various channels to the deuteron spin asymmetry and the double polarization E asymmetry is calculated. In addition, the contribution to the Gerasimov-Drell-Hearn (GDH) integral from separate channels is evaluated by explicit integration up to a photon lab energy of 350 MeV. Sizeable effects from final-state interactions, specially for π0 production, are found. The sensitivity of the results to the elementary pion photoproduction operator is also investigated. Considerable dependence of the results on the elementary amplitude is found. We expect that these results may be useful to interpret the recent measurements from LEGS@BNL, A2, and GDH@MAMI Collaborations.