Abstract
A next step in development of the KrkNLO method of including complete NLO QCD corrections to hard processes in a LO parton-shower Monte Carlo (PSMC) is presented. It consists of generalisation of the method, previously used for the Drell-Yan process, to Higgs-boson production. This extension is accompanied with the complete description of parton distribution functions (PDFs) in a dedicated, Monte Carlo (MC) factorisation scheme, applicable to any process of production of one or more colour-neutral particles in hadron-hadron collisions.
Highlights
The method of including complete NLO QCD corrections to hard processes in the leading order (LO) parton-shower Monte Carlo (PSMC), nicknamed KrkNLO, was originally proposed in Ref. [1], where its first numerical implementation on top of a toy-model PSMC was presented
In the version of Ref. [1], the MC weight implementing the NLO corrections sums the contributions from all relevant partons generated in PSMC next to the hard process “democratically”, such that it works well for PSMCs based on angular ordering or virtuality ordering, contrary to POWHEG which requires adding extra gluons to a PSMC event
In the KrkNLO method, the entire event of PSMC is preserved and reweighted, contrary to POWHEG and MC@NLO where the parton attributed to the hard process is generated outside PSMC and, only later on, the remaining partons are provided by PSMC
Summary
The method of including complete NLO QCD corrections to hard processes in the LO parton-shower Monte Carlo (PSMC), nicknamed KrkNLO, was originally proposed in Ref. [1], where its first numerical implementation on top of a toy-model PSMC was presented. These elements of the transition matrix have to be added for any process with initialstate gluons, such as the Higgs-boson production elaborated in the present work They will be defined and applied in the following, such that the complete transition matrix K transforming the MS PDFs into the MC-scheme PDFs will be specified for the first time. [1,2], the essence of the KrkNLO method is that certain NLO correction terms in an unintegrated/exclusive form present in the MS scheme, which are proportional to unphysical Dirac-delta terms in transverse momentum of emitted real partons, are removed in the KrkNLO methodology by means of redefinition of PDFs from the MS to MC scheme These ‘pathological’ terms are preventing the use of a simple multiplicative MC weight for implementing NLO corrections in the MS scheme in real-emission phase space, and they complicate implementation of the MC@NLO and POWHEG methods. In Appendix A the formulae for the NLO coefficient functions of the DIS process in the MC scheme are provided
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