Jets and Jet Multiplicities in High Energy Photon-Nucleon Inetraction:
  We discuss the theory of jet events in high-energy photon-proton interactions using a model which gives a good description of the data available on total inelastic $\gamma p$ cross sections up to $\sqrt{s}$=210 GeV. We show how to calculate the jet cross sections and jet multiplicities and give predictions for these quantities for energies appropriate for experiments at the HERA $ep$ collider and for very high energy cosmic ray observations. 
L. Durand, K. Honjo, R. Gandhi, I. Sarcevic and H. Pi