Colour Coherence in Photon Induced Reactions
  Colour coherence in hard photoproduction is considered using the Monte Carlo event generators PYTHIA and HERWIG. Significant effects in the parton shower are found using multijet observables for direct and resolved photon induced reactions. The particle flow in the interjet region of direct processes shows a strong influence of string fragmentation effects. 
A. Lebedev, L. Sinclair, E. Strickland, J. Vazdik