Why are the diffraction minima in π+ and π- scattering from 12C so different

The newly observed difference between π+ and π- elastic differential cross sections is shown to be a consequence of Coulomb distortion. Good agreement with the data is obtained at the first minimum by assuming the additivity of the Coulomb and nuclear phases in impact parameter space and an approximate formula is derived to describe the behaviour there. From this it can be seen that the sign of the π+,π- difference allows one to eliminate one of the ambiguities in a phase shift analysis. (Auth.)