  Through a direct analysis of the scattering amplitude, we show that the
preliminary measurement of the analysing power AN obtained by the E950
Collaboration at different energies are mainly sensitive to the spin-flip part
of the amplitude in which the proton scatters with the carbon 12 nucleus as a
whole. The imaginary part of this amplitude is negative, and the real part
positive. We give predictions for pL = 600 GeV/c, which depend mainly on the
size of the real part of the amplitude.
