DISPERSIVE EFFECTS FROM A COMPARISON OF ELECTRON AND POSITRON SCATTERING FROM C-12

Dispersive effects have been investigated by comparing elastic scatter ing of electrons and positrons from C-12 at the Saclay Linear Accelera tor. The results demonstrate that dispersive effects at energies of 26 2 MeV and 450 MeV are less than 2% below the first diffraction minimum [0.95<q(eff) (fm(-1))<1.66] in agreement with the prediction of Friar and Rosen. At the position of this minimum (q(eff)=1.84 fm(-1)), the deviation between the positron scattering cross section and the cross section derived from the electron results is -44%+/-30%. [S0556-2813(9 8)04405-7].