Elastic proton scattering at high momentum transfer as test of a microscopic optical potential

Measurements of the differential cross section for 200 MeV proton scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ have been extended to momentum transfers between 4 and 6 ${\mathrm{fm}}^{-1\mathrm{}}$. These new results are in disagreement with the parameter-free, microscopic optical potential model of Brieva, Rook, and Geramb, which satisfactorily reproduces the data at smaller momentum transfer. Calculations within the framework of a phenomenological optical potential also have difficulty explaining all of the structure observed in the large-angle region; the latter is very sensitive to changes of the potential at small radii.