A Positive-Weight Next-to-Leading Order Monte Carlo Simulation for Higgs Boson Production

TL;DR

This paper presents a positive-weight NLO Monte Carlo simulation for Higgs boson production that accurately incorporates full NLO corrections within the Herwig++ event generator, improving simulation reliability without negative weights.

Contribution

It introduces a novel positive-weight NLO matching scheme with full truncated shower implementation in Herwig++, validated against existing methods.

Findings

Simulation results agree with previous independent POWHEG studies.

Full NLO corrections are incorporated without negative weights.

Validation confirms the accuracy of the truncated shower implementation.

Abstract

In this article we describe simulations of Higgs boson production via the gluon fusion and Higgs-strahlung processes, using the positive weight next-to-leading-order (NLO) matching scheme, POWHEG, in the Herwig++ 2.3 event generator. This formalism consistently incorporates the full NLO corrections to these processes within the parton shower simulation, without the production of negative weight events. These simulations include a full implementation of the truncated shower required to correctly model soft emissions in an angular-ordered parton shower. We present a thorough validation of these simulations, comparing them to other methods and calculations. The results obtained for the gluon fusion process corroborate, and provide detailed explanations for, findings reported by Alioli et al (arXiv:0812.0578) using an independent POWHEG simulation, neglecting truncated shower effects, released at the same time as our code.