Abstract
Universality in QCD factorization of parton densities, fragmentation functions, and soft factors is endangered by the process dependence of the directions of Wilson lines in their definitions. We find a choice of directions that is consistent with factorization and that gives universality between annihilation, semi-inclusive deep-inelastic scattering, and the Drell-Yan process. Universality is only modified by a time-reversal transformation of the soft function and parton densities between Drell-Yan and the other processes, whose only effect is the known reversal of sign for -odd parton densities such as the Sivers function. The modifications of the definitions needed to remove rapidity divergences with lightlike Wilson lines do not affect the results.
- Received 23 August 2004
DOI:https://doi.org/10.1103/PhysRevLett.93.252001
©2004 American Physical Society