Rescattering corrections in radiative pion absorption

Abstract

Rescattering corrections to radiative pion absorption in nuclei are considered. The rescattering process is known to make important contributions to the nuclear absorption of S orbit pions with two-nucleon ejection. We calculate the rescattering corrections both in perturbation theory and with an approach based on the actual pion-nucleus scattering length. For the detailed evaluation of nuclear matrix elements the particle-hole formalism is used, and it is assumed that odd-parity spin-isospin nuclear states are excited by the radiative absorption mechanism. The calculation shows that incoherent rescattering effects involving an excited nucleus in the intermediate state are of little importance. Retaining only the coherent rescattering, decreases are found in the transition rate of approximately 40% relative to the leading term for 16O. The relationship between our calculation and analyses based on the use of an optical potential is presented.