The MC@NLO Package
Stefano Frixione, Fabian Stoeckli, Paolo Torrielli, Bryan Webber, Chris White
MC@NLO is a Fortran package to implement the eponymous scheme 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 or C++ Herwig++ event generator.
The current version is MC@NLO 4.0, released on 3 October 2010. This is a major upgrade of MC@NLO 3.42 (released on 16 June 2010). The main difference with respect to previous versions is that in the present one all processes can be simulated either with Fortran HERWIG, or with Herwig++, with the exception, in the latter case, of single-top in association with a charged Higgs, and of b quark pair production. Single-top production in association with a charged Higgs has been added since version 3.4, including spin correlations which were not previously implemented. The present version includes the upgrades of sub-versions 3.41 and 3.42. For precise details of version changes, please see the manual.
Sub-version 4.01, released on 4 April 2011, fixes a bug in Ht production, diagram removal definition, which may have caused an infinite loop to occur when computing spin correlations.
In sub-version 4.02, released on 15 June 2011, we have updated the code for Higgs production by gluon fusion, in order to give the user the possibility of treating the Higgs width in three different ways. This is done by means of the new input variable IWIDTHHGG. If one sets it equal to zero, one will get the same results as before (the code being strictly identical). On the other hand, by setting IWIDTHHGG=1, one will use a mass-dependent Higgs width, according to the prescription of M. Seymour, Phys.Lett.B354:409-414,1995. In such a case, the program will compute the width automatically; also, the branching ratio of the selected decay mode (e.g., WW when IPROC=-1610) will be included in the short-distance cross section, although the hard-event file will still contain only the Higgs. This implies that if one needs to decay the Higgs with another mode (say, ZZ), the hard-event file must be regenerated. Finally, by setting IWIDTHHGG=2 one will use the prescription called "Pythia/POWHEG" in sect. 11.4 of the "Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables" (eprint 1101.0593). Decay branching ratios are not included in this case.
Sub-version 4.03, released on 22 July 2011, contains minor bug fixes which do not affect any physics.
In sub-version 4.04, released on 9 December 2012, Ht production can also be simulated with Herwig++. In keeping with all the other processes, the same inputs as for the simulation with Herwig6 (including IPROC) are used in MCatNLO.inputs, except for the setting of MCMODE. Minor changes were also made in mcatnlo_hwlhin.f and mcatnlo_hwdriver.f, which may have caused problems (owing to different input conventions) when linking to modern versions of LHAPDF during the MC runs.
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 or charged Higgs), lepton pair and associated Higgs+W/Z production in hadron collisions.
This version is compatible with Fortran HERWIG 6.5 or higher, which can be obtained from the HERWIG home page. Use of version 6.520 or higher is strongly recommended. See also the HERWIG wiki for latest news and updates.
This version is also compatible with Herwig++, which can be obtained from the Herwig++ home page. The user will have to provide installed versions of Herwig++ and ThePEG. We advise the user to adopt versions 2.4.2 for Herwig++ and 1.6.1 for ThePEG or later. We stress that the options ReconstructionOption=General and InitialInitialBoostOption=LongTransBoost must be used when running Herwig++. These are automatically set by our script, and the user must not change them. The latter option is presently available only in the trunk version of Herwig++ 2.4.2.
Here you can find
- The MC@NLO 4.04 package (gzipped tar file);
- The MC@NLO 4.0 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);
- The article JHEP01(2011)053 describing the implementation for Herwig++ (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].
- S. Frixione, F. Stoeckli P. Torrielli and B.R. Webber, NLO QCD corrections in Herwig++ with MC@NLO, JHEP 1101 (2011) 053 [arXiv:1010.0568].
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 09/12/11
