The MC@NLO 3.1 Event Generator

TL;DR

MC@NLO 3.1 presents a practical workflow to embed NLO QCD matrix elements into a parton-shower framework by coupling NLO calculations to the HERWIG generator via the Les Houches interface. It expands the process set to include Higgs production, vector-boson pairs, heavy quark pairs, and leptonic final states, with spin correlations for most decays. The package introduces a two-stage workflow: an NLO stage that builds an event file of hard configurations and an MC stage that showers these events, accounting for negative-weight events inherent to MC@NLO. It requires careful handling of PDFs (PDFLIB or internal library, LHAPDF not supported in 3.1) and a consistent parameter set across NLO and MC runs. The practical distribution includes extensive scripts and process-specific codes, along with detailed user instructions for running with or without shell scripts.

Abstract

This is the user's manual of MC@NLO 3.1. This package is a practical implementation, based upon the HERWIG event generator, of the MC@NLO formalism, which allows one to incorporate NLO QCD matrix elements consistently into a parton shower framework. Processes available in this version include the hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy quark pairs, lepton pairs, and Higgs bosons in association with a W or Z. Spin correlations in decays are included for all processes except ttbar, ZZ, and WZ production. This document is self-contained, but we emphasise the main differences with respect to previous versions.