Evidence for spin-spin effects in p-->-13C elastic scattering

The depolarization parameter D in proton-¹³C elastic scattering at 72 MeV has been measured with an accuracy of 0.003-0.004 per data point. D was found to deviate from unity by ~0.02 around 65°, which is unambiguous evidence for a nucleon-nucleus spin-spin interaction. The data are well described by a microscopic calculation as well as by a phenomenological optical-model potential, which includes a real spherical spin-spin potential of strength V_ss=0.7+/-0.1 MeV.