A critical appraisal of NLO+PS matching methods

TL;DR

This paper critically compares NLO+PS matching methods MC@NLO and POWHEG, analyzing their uncertainties and impacts on observables in Higgs and vector boson production, with new results on H+jet simulation.

Contribution

It provides a detailed comparison of MC@NLO and POWHEG methods, including implementation details and their effects on various collider observables, introducing the first NLO+PS simulation of H+jet production.

Findings

Differences in uncertainties between MC@NLO and POWHEG are quantified.

The impact of phase space restrictions on radiative corrections is analyzed.

First NLO+PS simulation results for H+jet production are presented.

Abstract

In this publication, uncertainties in and differences between the MC@NLO and POWHEG methods for matching next-to-leading order QCD calculations with parton showers are discussed. Implementations of both algorithms within the event generator Sherpa and based on Catani-Seymour subtraction are employed to assess the impact on a representative selection of observables. In the case of MC@NLO a substantial simplification is achieved by using dipole subtraction terms to generate the first emission. A phase space restriction is employed, which allows to vary in a transparent way the amount of non-singular radiative corrections that are exponentiated. Effects on various observables are investigated, using the production of a Higgs boson in gluon fusion, with or without an associated jet, as a benchmark process. The case of H+jet production is presented for the first time in an NLO+PS matched simulation. Uncertainties due to scale choices and non-perturbative effects are explored in the production of W and Z bosons in association with a jet. Corresponding results are compared to data from the Tevatron and LHC experiments.