  We study the Collins mechanism for the single transverse spin asymmetry in
the collinear factorization approach. The correspondent twist-three
fragmentation function is identified. We show that the Collins function
calculated in this approach is universal. We further examine its contribution
to the single transverse spin asymmetry of semi-inclusive hadron production in
deep inelastic scattering and demonstrate that the transverse momentum
dependent and twist-three collinear approaches are consistent in the
intermediate transverse momentum region where both apply.

High Energy Physics - Phenomenology