NN Final-State Interaction in the Helicity Dependence of Inclusive   $\pi^-$ Photoproduction from the Deuteron
  The helicity dependence of the inclusive $\pi^-$ photoproduction reaction from the deuteron in the $\Delta$(1232)-resonance region is investigated with inclusion of final-state nucleon-nucleon rescattering ($NN$-FSI). For the elementary $\pi$-production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a contribution from the $\Delta$-resonance is used. The half-off-shell $NN$-scattering matrix is obtained from a separable representation of a realistic $NN$-interaction. The differential polarized cross-section difference for parallel and antiparallel helicity states is predicted and compared with experiment. We find that the effect of $NN$-FSI is much less important in the helicity difference than in the previously studied unpolarized differential cross section. Furthermore, the contribution of $\vec d(\vec\gamma,\pi^-)pp$ to the deuteron spin asymmetry is explicitly evaluated with inclusion of $NN$-FSI. It has been found that the effect of $NN$-FSI is much larger in the asymmetry than in the total cross section, and this leads to an appreciable reduction of the spin asymmetry in the $\Delta$-region. Inclusion of such effect also leads to improved and quite satisfactory agreement with existing experimental data. 
Eed M. Darwish (South Valley University, Sohag)