=== How do I implement my own renormalization/factorization scales in !MadEvent? ===
Since v.4.2.17, there is a new default dynamical scale choice in run_card.dat file:
{{{
#*********************************************************************
# Renormalization and factorization scales *
#*********************************************************************
F = fixed_ren_scale ! if .true. use fixed ren scale
F = fixed_fac_scale ! if .true. use fixed fac scale
91.1880 = scale ! fixed ren scale
91.1880 = dsqrt_q2fact1 ! fixed fact scale for pdf1
91.1880 = dsqrt_q2fact2 ! fixed fact scale for pdf2
1 = scalefact ! scale factor for event-by-event scales
}}}
i.e., variable factorization and renormalization scales,set to the central mT^2 scale after kT-clustering of the event.
For a single heavy particle, this corresponds to the M^2+pT^2,
for pair of heavy particles it is the geometric mean of M^2+pT^2 for each particle,
for massless particles it is the pT^2 of the last pair after clustering.
If the last clustering is a t-channel colorless exchange (as, e.g., in WBF), the two fact. scales are set to the last mT^2 values on either side.
These scales are overridden by scales defined in [http://bazaar.launchpad.net/~madteam/madgraph5/trunk/view/head:/Template/SubProcesses/setscales.f setscales.f], if they are returned as non-0.
Fixed values for the scale (not event-by-event) can be set in the same file, by setting the two flags
{{{
fixed_ren_scale, fixed_fac_scale
}}}
to True and choosing the desired value for them :
{{{
scale, dsqrt_q2fact1, dsqrt_q2fact2
}}}
If the user wants to have a different choice for the dynamical scale, one needs
1. to know a bit of fortran
2. to download the code (either after process generation or from our Download page) and run on your local machine.
The file to be edited is [http://bazaar.launchpad.net/~madteam/madgraph5/trunk/view/head:/Template/SubProcesses/setscales.f SubProcesses/setscales.f].
-- Main.FabioMaltoni - 02 Mar 2009