Semi-Exclusive Pion Production in Deep-Inelastic Scattering
  We calculate azimuthal asymmetries and the Callan-Gross $R$-ratio for semi-exclusive pion production in deep inelastic scattering taking into account higher twist effects. Our results are qualitatively different from the QCD-improved parton model predictions for semi-inclusive deep inelastic scattering. 
A. Brandenburg, V. V. Khoze and D. M\"uller