Multiple scattering theory for pion-nucleus elastic scattering and the in-medium piN amplitude

Elastic scattering of positive and/or negative pions (pi+ and/or pi-) by nuclei has been studied by means of Glauber's multiple scattering theory (GMST). The differential, total and total elastic cross sections using both the full series expansion and the first order correction (called optical limit results, OLA) of the Glauber amplitude, have been calculated. The in-medium pN amplitude (sigmaeff., sigmaeff.) as well as the free piN one (sigmafree, sigmafree) are invoked into the full series calculations of the Glauber amplitude and our results were compared with the corresponding experimental data. These calculations are carried out for the elastic collisions, pi-- 2He4 at incident energy 180 MeV, pi±- 3Li6 at 240 MeV, pi-- 6C12 at incident energies 180, 200 and 260 MeV, pi+- 8O16 at 240 and 270 MeV and pi±- 20Ca40 at energy 292.5 MeV. The comparisons reflect that, except around the minima, the full series calculations with the in-medium pN amplitude are better in describing the scattering data than those using the free piN one and both are better than the optical limit results.