Optical-Model Analysis of Pion-Nucleus Scattering

Determination of nuclear-density parameters and of the rms pion charge radius r_π from the elastic scattering of pions by nuclei has been studied using the optical model proposed by Kisslinger. Good fits to the available data in the kinetic-energy region 24 MeV≤T_π≤153 MeV have been found by searching the parameter space. For T_π≈80 MeV, i.e., T_π large compared to nuclear binding energies but well below the N* resonance, the best-fit parameters are close to those predicted from pion-nucleon phase shifts. The nuclear radii obtained are consistent with electron-scattering radii; the calculated differential cross sections are sensitive to a second nuclear-density parameter for large angles. "Distortion" of the Coulomb amplitude in 24-MeV π^±-α scattering reduces r_π from 1.8±{}0.8 F to r_π≤2.0 F (two standard deviations), in agreement with West's recent calculation.