Dispersive effects from a comparison of electron and positron scattering from $^{12}$C
Résumé
Dispersive effects have been investigated by comparing elastic scattering of electrons and positrons from $^{12}$C at the Saclay Linear Accelerator. The results demonstrate that dispersive effects at energies of 262 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 $–44\%\pm 30\%$.