Off-shell rescattering effects in the reactionπ−+d→2n+γ

We have reexamined the multiple scattering corrections to the reaction ${\pi }^{-}+d\to 2n+\gamma$ in order to extend the validity of previous calculations to a larger neutron-neutron relative momentum interval and to determine the effective range parameter. This extension has been carried out analytically by studying the off-shell properties and energy dependence of the pion-nucleon amplitude. The sensitivity of the photon spectral curves for various approximations is shown, and the importance of the different effects in the values of the neutron-neutron scattering length and effective range is indicated.