ON THE IMAGINARY PART OF THE S-WAVE PION NUCLEUS OPTICAL-POTENTIAL

The contribution of pion absorption to the imaginary part of the S-wave pion-nucleus optical potential is calculated with Slater determinantal antisymmetrized nuclear wave functions, taking fully into account the spin and isospin degrees of freedom. The potential obtained has an explicit dependence on the proton and neutron nuclear densities whose coefficients are directly related to the two-nucleon absorption coupling constants. The values of these coefficients extracted from mesic atoms data are in good agreement with those deduced from exclusive pion absorption experiments in He-3, but larger than the predictions of the pion rescattering model.