Single-spin azimuthal asymmetries in the “Reduced twist-3 approximation”

We consider the single-spin azimuthal asymmetries recently measured at the HERMES experiment for charged pions produced in semi-inclusive deep inelastic scattering of leptons off longitudinally polarized protons. Guided by the experimental results and assuming a vanishing twist-2 transverse quark spin distribution in the longitudinally polarized nucleon, denoted as “reduced twist-3 approximation”, a self-consistent description of the observed single-spin asymmetries is obtained. In addition, predictions are given for the z dependence of the single target-spin asymmetry.