### 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 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

- to know a bit of fortran
- 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 SubProcesses/setscales.f.

-- Main.FabioMaltoni - 02 Mar 2009