Contributions due to the longitudinal virtual photon in the   semi-inclusive ep collision at HERA
  The importance of contributions due to the longitudinally polarised virtual photon and the longitudinal-transverse interference term, in the unpolarised ep collisions is discussed. The numerical calculations for the Compton process, e p --> e gamma X, at the HERA collider were performed in the Born approximation. The various distributions in the ep centre-of-mass and Breit frames are presented. These cross sections are dominated by the transversely polarised intermediate photon, even for large values of its virtuality. 
Urszula Jezuita-Dabrowska (Institute of Theoretical Physics, Warsaw   University)