Influence of rescattering effects on the helicity dependence of γ→d→→πNN near threshold and its implication to the E-asymmetry and the GDH sum rule

This work deals with investigation of the helicity dependence of the γ → d → → π N N reaction channels near threshold and its implication to the helicity E-asymmetry and the Gerasimov-Drell-Hearn sum rule. Our formalism based on the one loop corrections to the impulse approximation due to nucleon and pion rescattering, uses the realistic Paris NN potential model for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary γN → πN amplitude. We present results for the doubly polarized differential and total cross sections for parallel and antiparallel helicity states, the deuteron spin asymmetry, the helicity E-asymmetry, and the deuteron GDH integral in the near-threshold region. The influence of NN and πN final-state rescattering on the estimated results has been discussed. It is shown that the inclusion of NN rescattering is important, and its inclusion strongly affected the estimated results in both π ± - and π0-production channels. The inclusion of πN rescattering is found to be insignificant in π ± -production, but it has a non- negligible contribution in the case of π0-production. A comparison with predictions of other theoretical models is given.