First measurement of the real part of a pp double-spin-flip amplitude.

The asymmetry ${A}_{\mathrm{NN}}$ for pp elastic scattering has been measured at 800 and 650 MeV in the region of Coulomb-nuclear interference. The data have been analyzed to extract the real part of a spin-spin scattering amplitude. Results are compared with the predictions of forward dispersion relations. They disagree significantly at 650 MeV.