Transverse single spin asymmetries in inclusive deep-inelastic   scattering
  In inclusive deep-inelastic lepton-hadron scattering multi-photon exchange between the leptonic and the hadronic part of the process causes single spin asymmetries. The asymmetries exist for a polarized target as well as a polarized incoming or outgoing lepton, if the polarization vector has a component transverse with respect to the reaction plane. The spin dependent parts of the single polarized cross sections are suppressed like $\alpha_{em} m_{pol}/Q$ - where $m_{pol}$ denotes the mass of the polarized particle - compared to the leading terms of the cross section for unpolarized or double-polarized deep-inelastic scattering. Both the target and the beam spin asymmetry are evaluated in the parton model. In the calculation only quark-quark correlators are included. While this approximation turns out to be justified for the lepton spin asymmetries, it is not sufficient for the target asymmetry. 
A. Metz, M. Schlegel, and K. Goeke