Last modified 5 years ago Last modified on 04/24/12 11:09:54

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 mT2 scale after kT-clustering of the event. For a single heavy particle, this corresponds to the M2+pT2, for pair of heavy particles it is the geometric mean of M2+pT2 for each particle, for massless particles it is the pT2 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 mT2 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

  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 SubProcesses/setscales.f.

-- Main.FabioMaltoni - 02 Mar 2009