Dynamics of Multijet Processes in Photoproduction
  The cross section for producing three high transverse energy jets with a three-jet invariant mass of M_3J > 50 GeV has been measured in photoproduction at HERA. The angular distribution of the three jets is presented and found to be inconsistent with a uniform population of the available phase space. In contrast, parton shower models and O(alpha alpha_s^2) pQCD calculations are able to describe the three jet dynamics. 
L. E. Sinclair (for the ZEUS Collaboration)