Theory of Angular Correlations for Two Nucleons Emitted in the Nuclear Absorption of Slow Pions

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Abstract
A theory is developed for the angular correlation for two fast nucleons emitted when a nucleus absorbs a slow pion, based on the assumption that the reaction is direct. It is shown that for a quite general class of models for the two-nucleon absorption mechanism, there are selection rules which relate the final angular momenta of the two nucleons to the angular momenta carried initially by the two nucleons in the target nucleus. The selection rules involve the relative and center-of-mass motions, separately, of the nucleon pair. The angular correlation of interest is therefore defined with respect to the angle between the relative and c.m. momenta of the emitted nucleons. The selection rules provide a direct connection between the observed angular correlation and the two-nucleon angular momentum structure of the target nucleus. Some examples are given for the application of this theory to the study of nuclear structure.