Extraction of γn → πN observables from deuteron-target data

An examination is conducted on a commonly used procedure for extracting (un)polarized gamma n -> pi(-) p and gamma n -> pi(0)n observables from H-2(gamma, pi(-))pp and H-2(gamma, pi(0))pn data, using a model that consists of the impulse term and the final-state interaction (FSI) terms due to nucleon and pion exchange. Recent experimental and theoretical analyses used an extraction method that does not impose a cut on the final pi N invariant mass W. I demonstrate that the use of this method can result in the gamma n -> pi N observables that are seriously distorted by the nucleon Fermi motion, and that one can efficiently avoid this problem by imposing a cut on W. It is also shown that the use of kinematical cuts of recent experimental analyses can still leave in the selected samples substantial FSI effects that must be corrected in extracting the gamma n -> pi N cross sections. In terms of the nucleon- and pion-exchange mechanisms, I give the first qualitative explanation of the FSI corrections, obtained in a recent Mainz Microtron experiment, for extracting gamma n -> pi(0)n cross sections.