Need for fully unintegrated parton densities
  Associated with the use of conventional integrated parton densities are kinematic approximations on parton momenta which result in unphysical differential distributions for final-state particles. We argue that it is important to reformulate perturbative QCD results in terms of fully unintegrated parton densities, differential in all components of the parton momentum. 
John Collins (Physics Department, Penn State University, USA), Hannes   Jung (DESY, Hamburg, FRG)