These notes are to help run MCFM as part of the CDF software. Currently, MCFM v2.0 and v3.4.5 are integrated with the CDF software. Newer versions for stand-alone running and detailed documentation and references can be found here.

MCFM can run in leading-order (LO) or next-to-leading-order (NLO) modes. The instructions here are for running MCFM at LO, providing events for parton showering by Pythia.

Only WW production and decay to leptons has been extensively investigated using MCFM interfaced to Pythia. It may be straightforward to generate other processes but the interface to Pythia will likely need modifying in such cases.

Step-by-step instructions for MCFM v2.0 :

1. linux> source ~cdfsoft/cdf2.cshrc
2. linux> setup cdfsoft2 4.9.1
3. linux> newrel -t 4.9.1 mcfm_test; cd mcfm_test
4. linux> addpkg generatorMods
5. linux> cvs update -r 1.5 generatorMods/examples/mcfm/mcfm.tcl
6. linux> addpkg mcfm anom_coup                     [-> note the special tag for the mcfm package]
7. linux> gmake nobin
8. linux> gmake generatorMods.bin                    [-> this will make the "cdfGen" executable]
9. linux> cp mcfm/Bin/*.DAT .                            [-> mcfm needs these control files in the test release where you are working]
10. linux> cp mcfm/Bin/*.dat .                               [-> mcfm needs these data files to run properly]
11. lunux> ./bin/Linux2-KCC_4_0/cdfGen generatorMods/examples/mcfm/mcfm.tcl

Step-by-step instructions for MCFM v3.4.5 :

1. linux> source ~cdfsoft/cdf2.cshrc
2. linux> setup cdfsoft2 4.9.1
3. linux> newrel -t 4.9.1 mcfm_test; cd mcfm_test
4. linux> addpkg generatorMods
5. linux> cvs update -r 1.4 generatorMods/src/MCFM_Module.cc
6. linux> cvs update -r 1.3 generatorMods/generatorMods/MCFM_Module.hh
7. linux> cvs update -r 1.5 generatorMods/examples/mcfm/mcfm.tcl
8. linux> addpkg mcfm mcfm_345                       [-> note the special tag for mcfm v3.4.5]
9. linux> gmake nobin
10. linux> gmake generatorMods.bin                    [-> this will make the "cdfGen" executable]
11. linux> cp mcfm/Bin/* .                                      [-> mcfm needs these control files in the directory in which it is being run]
12. lunux> ./bin/Linux2-KCC_4_0/cdfGen generatorMods/examples/mcfm/mcfm.tcl

Notes :

• In the case of the above tcl file, the output file containing HEPG banks is "mcfm_ww_hepg_10k_4.root" (although it only contains 100 events).
• All other CDF simulation programs that link the standard set of generators should also work with MCFM.
• MCFM itself only generates dielectron events for process code 61 (WW->evev). The Pythia interface substitutes muons or taus at random in the correct proportions.
• Taus are decayed by tauola - see the tcl file for more details.
• The tcl file deals mainly with setting up the parameters for Pythia parton showering. All the relevant MCFM parameters including the center of mass energy are in "options.DAT".
• The cross section is reported by MCFM. Note that it is the cross section for the underlying MCFM process (e.g. WW->evev) in femtobarns, and needs to be multiplied by appropriate factors to obtain the inclusive cross section. The cross section is leading order. MCFM must be run stand-alone in NLO mode in order to generate NLO cross section estimates.
• At leading order all weights generated by MCFM are positive. The Pythia interface unweights the events, so there should be no need to keep track of relative event weights.
• There is limited documentation for running MCFM in NLO mode provided in "mcfm/scripts/run_mcfm". Refer also to the documentation provided by the authors.
• WW PRODUCTION WITHOUT SPIN CORRELATIONS:follow the instructions exactly as above, but with the following small differences :
• v2.0 : add the package mcfm with tag "anom_coup_nospin" instead of "anom_coup".
• v3.4.5 : select process 64 rather than 61 in the input.DAT file.