The MC@NLO 3.4 Event Generator

TL;DR

MC@NLO 3.4 provides a practical framework to embed NLO QCD matrix elements into a HERWIG-based parton shower, enabling precise, event-level predictions for a wide set of hadronic processes. The workflow separates NLO event generation (producing a Les Houches event file) from the subsequent HERWIG shower/hadronization, with careful handling of negative-weight events and spin correlations across most processes. Key additions in this release include explicit Wt production handling (diagram removal/subtraction), spin-correlated top decays, improved LHAPDF integration, and broader process coverage (including single-top and associated Higgs production). The manual emphasizes modular linking to external PDF libraries, detailed input control via MCatNLO.inputs, and robust guidance for running with shell scripts, making MC@NLO accessible for phenomenology studies at colliders while highlighting caveats for certain ill-defined cross sections and spin-correlation limitations.

Abstract

This is the user's manual of MC@NLO 3.4. 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, single top, single top in association with a W, lepton pairs, and Higgs bosons in association with a W or Z. Spin correlations are included for all processes except ZZ and WZ production. This document is self-contained, but we emphasise the main differences with respect to previous versions.