Subleading-twist effects in single-spin asymmetries in semi-inclusive   deep-inelastic scattering on a longitudinally polarized hydrogen target
  Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the subleading-twist contribution to the longitudinal case. This contribution is significantly positive for (\pi^+) mesons and dominates the asymmetries on a longitudinally polarized target previously measured by \hermes. The subleading-twist contribution for (\pi^-) mesons is found to be small. 
The HERMES Collaboration: A. Airapetian: et al