Abstract :
We illustrate, in a simple physical picture, how an axial asymmetry in impact parameter dependent parton distributions, in combination with final state interactions, can give rise to an axial asymmetry for the transverse momentum of the leading quark in the photo-production of hadrons. The effect is related to the asymmetry originating from the Wilson-line phase factor in gauge invariant Sivers distributions. We also explain the correlation between the sign of the anomalous magnetic moment and the sign of the Sivers asymmetry.
