Threshold charged-pion photoproduction and radiative pion capture. II.π−d→γnn

The transition operator for threshold charged-pion photoproduction and radiative pion capture is utilized in its nonrelativistic limit to calculate the absolute rate for the ${\pi }^{-}d\to \gamma \mathrm{nn}$ reaction from a $1s$ atomic orbital in the impulse approximation. Sensitivity to assumptions concerning the initial state of the ${\pi }^{-}d$ system and the short-range character of the $n-n$ wave function in the final state is discussed, as is the relevance of the absolute rate to the determination of the $n-n$ scattering length from this reaction.