The MC@NLO 3.2 Event Generator

TL;DR

MC@NLO 3.2 provides a practical framework for combining NLO QCD matrix elements with a HERWIG parton shower via the Les Houches interface, covering a broad set of hadroproduction processes including vector bosons, Higgs, heavy quarks, single top, lepton pairs, and associated Higgs production. The workflow uses a two-step approach: an NLO calculation generates an event file of hard subprocess configurations, and a subsequent MC run showers these events, with negative-weight events requiring signed-weight handling. The manual details the required file structure, environment setup, PDF options (PDFLIB, LHAPDF, or an internal library), and the script-driven inputs (MCatNLO.inputs) that control run parameters, decays, and outputs. Version 3.2 adds single-top production and LHAPDF support, clarifies differences from prior releases, and provides extensive guidance on running with compatible HERWIG versions and managing large data/event files for efficient computation.

Abstract

This is the user's manual of MC@NLO 3.2. 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, lepton pairs, and Higgs bosons in association with a W or Z. Spin correlations in decays are included for all processes except ttbar, single-t, ZZ, and WZ production. This document is self-contained, but we emphasise the main differences with respect to previous versions.