"Optical" Spin Rotation Phenomenon and Spin Filtering of Antiproton   (Proton, Deuteron) Beams in a Pseudomagnetic Field of a Polarized Target: the   Possibility of Measuring the Real Part of the Coherent Zero-angle Scattering   Amplitude
  It is shown that in the experiments dedicated for producing of polarized beams of antiprotons during their passage through a polarized gas target placed in a storage ring it is possible to measure not only spin-dependent total cross-sections of antiproton scattering by the proton (deuteron), but also the spin-dependent real part of the coherent zero-angle scattering amplitude in the process of production of a polarized beam of antiprotons. 
V.G. Baryshevsky
hep-ph