Subtraction method for NLO corrections in Monte-Carlo event generators for Z boson production

TL;DR

This work applies Collins' subtraction method to NLO corrections in Monte-Carlo event generators for Drell-Yan vector boson production, comparing two parton-shower algorithms (BSZ and a Collins-modified New algorithm). It derives unsubtracted and subtracted NLO terms for the gluon–quark subprocess and analyzes the relation of generator PDFs to the MSbar scheme, finding a DIS-like PDF relation for the New algorithm but not for BSZ due to correlated kinematics. The paper also extends the treatment to W production and discusses the implications for implementing NLO corrections in MC tools like PYTHIA/RAPGAP. Overall, it clarifies scheme dependence and provides a consistent subtraction framework for incorporating NLO effects in vector boson production within MC generators.

Abstract

We use a subtraction method to construct NLO corrections in a Monte-Carlo event generator for the case of vector boson production in Drell-Yan processes. Our calculations are carried out both for the Bengtsson-Sjostrand-van Zijl (BSZ) algorithm and for a modified algorithm proposed by Collins. In the case of the modified algorithm, we compute the relation between the parton distribution functions and the ones in the MSbar scheme; this relation is the same as the corresponding relation for DIS. For the BSZ algorithm, we show that there is no simple relation.