Single spin asymmetry at large xF and kperpendicular

The large single spin asymmetries observed at high momentum fractions xF and transverse momenta kperpendicular in pp→π(xF,kperpendicular)+X as well as in pp→Λ(xF,kperpendicular)+X suggest that soft helicity flip processes are coherent with hard scattering. Such coherence can be maintained if xF→1 as kperpendicular→∞, while kperpendicular2(1-xF) ∼ ΛQCD2 stays fixed. The entire hadron wave function, rather than a single quark, then contributes to the scattering process. Analogous coherence effects have been seen experimentally in the Drell-Yan process at high xF. We find that the pp→π(xF,kperpendicular)+X production amplitudes have large dynamic phases and that helicity flip contributions are unsuppressed in this limit, giving rise to potentially large single spin asymmetries