Depolarization in elastic proton scattering and the nucleon-nucleus spin-spin interaction

Abstract The depolarization parameter D in proton- 13 C elastic scattering at 72 MeV has been measured at 34° ⩽ θ c .m. ⩽ 69° with an overall accuracy of (3–4) × 10 −3 . Significant deviations from D = 1 were observed around 65°. This finding constitutes unambiguous evidence for a nucleon-nucleus spin-spin interaction. The data were fitted by a conventional optical model potential which included a real, spherical spin-spin potential with surface form factor and V ss = 0.7 ± 0.1 MeV. Good description of the data was also obtained by a microscopic calculation which was based on a density dependent, effective interaction and shell model wave-functions. Similar calculations for 9 Be, 15 N, 29 Si and 31 P are consistent with recent data. In particular, they explain the large effects observed for 15 N.