The MC@NLO 4.0 Event Generator

TL;DR

MC@NLO 4.0 delivers a robust framework for matching NLO QCD matrix elements to parton showers, supporting a wide range of production processes and enabling spin correlations, Wt/Ht definitions, and WZ anomalous couplings within both HW6 and HW++ environments. The package emphasizes an event-file workflow via the Les Houches interface, flexible PDF handling with LHAPDF, and explicit treatment of uncertainties and decays, while maintaining backward-compatible structures and detailed user controls through MCatNLO.inputs. The combination of enhanced process coverage, divisor-level control of decays and couplings, and LHAPDF integration significantly improves the practicality and precision of NLO+PS event generation for collider phenomenology. This release thus provides a versatile, extensible tool for generating realistic, fully showered events with NLO accuracy across a broad spectrum of Standard Model processes and beyond.

Abstract

This is the user's manual of MC@NLO 4.0. This package is a practical implementation, based upon the Fortran HERWIG and Herwig++ event generators, 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, single top in association with a charged Higgs in type I or II 2HDM models, lepton pairs, and Higgs bosons in association with a W or Z. Spin correlations are included for all processes except ZZ production. This document is self-contained, but we emphasise the main differences with respect to previous versions.