NLL order contributions for exclusive processes in jet-calculus scheme

We investigate the next-to-leading logarithmic (NLL) order contributions of the quantum chromodynamics (QCD) for exclusive processes evaluated by Monte Carlo methods. Ambiguities of the Monte Carlo calculation based on the leading-logarithmic (LL) order approximations are pointed out. To remove these ambiguities, we take into account the NLL order terms. In a model presented in this paper, interference contributions due to the NLL order terms are included for the generation of the transverse momenta in initial-state parton radiations. Furthermore, a kinematical constraint due to parton radiation, which is also a part of the NLL order contributions, is taken into account. This method guarantees a proper phase space boundary for hard scattering cross sections as well as parton radiations. As an example, cross sections for lepton pair productions mediated by a virtual photon in hadron-hadron collisions are calculated, using the jet-calculus scheme for flavor nonsinglet quarks. (author)