The MC@NLO Package

Stefano Frixione, Bryan Webber

MC@NLO is a Fortran package to implement the scheme we have proposed for combining a Monte Carlo event generator with Next-to-Leading-Order calculations of rates for QCD processes.

MC@NLO makes use of the Fortran HERWIG event generator.

The current version is MC@NLO 3.41, released on 23 October 2009. This is a minor upgrade of MC@NLO 3.4 (released on 13 November 2008) with correction of a potential problem in top decays. In order to generate, say, 100K events, one may generate them in one run, or for example in 20 runs of 5K events each. In the latter case, and only in that case, the relative fractions of top decay products generated by version 3.4 may turn out to be incorrect. Basically, by changing the seed in each of the 20 runs the event kinematics were changed, but the identities of the decay particles were not. Our thanks to Frank Filthaut for uncovering this problem and proposing a fix, and to Gia Khoriauli for testing the new version.

The main differences between version 3.4 and the previous version (3.3) are: single top production in association with a W boson has been implemented; hadronic top decays are included; Root-format output can be generated; linking to LHAPDF has been upgraded; MC subtraction terms have been modified in such a way that b-bbar production at LHC may now be considered safe.

Users are reminded that in versions 3.1 onwards the format of the event file, produced by the `NLO' part of the package and read by the `MC' part, has been changed relative to earlier versions, and therefore event files created by versions 2.3 or earlier cannot be used with this version.

The processes available in this version are those of Higgs boson, single vector boson, vector boson pair, heavy quark pair, single top (with and without associated W), lepton pair and associated Higgs+W/Z production in hadron collisions.

This version is compatible with HERWIG 6.5 or higher, which can be obtained from the HERWIG home page. Use of version 6.510 or higher is strongly recommended. See also the HERWIG wiki for latest news and updates.

Here you can find

• The MC@NLO 3.41 package (gzipped tar file);
• The MC@NLO 3.4 manual (gzipped postscript, pdf);
• The article JHEP06(2002)029 describing the MC@NLO formalism (local copy);
• The article JHEP08(2003)007 describing the application to heavy quark pair production (local copy);
• The article JHEP03(2006)092 describing the application to single top production (local copy);
• The article JHEP07(2008)029 describing the application to tW production (local copy);
• A description (gzipped Postscript) and the grid files (gzipped tar file) of our parton density function library, which is a faster version of PFDLIB with many newer PDFs.
• A local copy of the original PDFLIB manual (gzipped Postscript), which you may need to refer to.

If you use MC@NLO, please cite the original publication:

• S. Frixione and B.R. Webber, Matching NLO QCD computations and parton shower simulations, JHEP 0206 (2002) 029 [hep-ph/0204244]

and those relevant from the following:

• S. Frixione, P. Nason and B.R. Webber, Matching NLO QCD and parton showers in heavy flavour production, JHEP 0308 (2003) 007 [hep-ph/0305252];
• S. Frixione, E. Laenen, P. Motylinski and B.R. Webber, Single-top production in MC@NLO, JHEP 0603 (2006) 092 [hep-ph/0512250];
• S. Frixione, E. Laenen, P. Motylinski, B.R. Webber and C.D. White, Single-top production in association with a W boson, JHEP 0807 (2008) 029 [arXiv:0805.3067].

The program by B. Fuks, M. Klasen, F. Ledroit, Q. Li and J. Morel implementing Z' production in MC@NLO can be found here.

Last updated BRW 23/10/09