wiki:FAQ-General-2

Version 4 (modified by md987, 8 years ago) (diff)

--

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 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 SubProcesses/setscales.f.

-- Main.FabioMaltoni - 02 Mar 2009