NLL Order Contributions for Exclusive Processes in Jet-Calculus Scheme

TL;DR

This paper enhances Monte Carlo QCD calculations for exclusive processes by incorporating NLL order contributions, reducing ambiguities, and ensuring proper phase space boundaries, demonstrated through lepton pair production cross sections.

Contribution

It introduces a method to include NLL order terms in Monte Carlo simulations, improving accuracy and resolving ambiguities present in LL approximations.

Findings

Inclusion of NLL terms improves phase space boundary accuracy.

Interference contributions are incorporated for transverse momentum generation.

Cross sections for lepton pair production are accurately calculated.

Abstract

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.