A number of popular dynamical scale choices have been implemented and they can be used as templates for implementing a new scale. If the desired factorization or renormalization scale is not in this list, the user can easily add it as follows.
Scales
in the file utilities/scales.F90 to
find out where to implement the new scales of the process at hand.
For example, for the class of VBF or VBS processes (\(Hjj\),
\(Vjj\), \(VVjj\)), the scales are calculated in the subroutine
calcVBFscales
, while it is
calcVXjScales
for diboson and triboson processes.
calcVBFscales
. The new
identification numbers for ID_MUF
and
ID_MUR
must be different from the ones already used.
A good practice is to use the same value for both scales. The
factorization-scale implementation reads
case(ID_MUF_NEW)
do L=1,Lmax
...
mufsq(1, L) = ...
mufsq(2, L) = ...
enddo
where Lmax
(already calculated by the program) is
the number of different kinematic configurations, which is
greater than unity when calculating the dipole-subtraction term
at NLO; mufsq(1,L)
is the square of the
factorization scale for the first hadron,
mufsq(2,L)
is for the second hadron. Similarly, for
the renormalization scale, we have
case(ID_MUR_NEW)
do L=1,Lmax
...
mursq(1, L) = ...
als(1, L) = ...
als(2, L) = ...
...
enddo
where mursq(1,L)
is the square of the
renormalization scale, the calculation of the strong coupling
constants als(i,L)
is the same as for the already
implemented cases. The values of mufsq(i,L)
,
mursq(i,L)
and als(i,L)
are then
transfered to other routines via the common block
cscales
in scales.inc.
make clean
command before VBFNLO is remade
and installed using the make
and
make install
commands from the program directory. The
new scales are then ready to be used by specifying the values of
the identification numbers in vbfnlo.dat.
Dynamical scales are calculated from the momenta of the external-state particles. The following momenta are available and ready to be used
p(i,j,L)
: 4-momenta of the partons.v(i,j,L)
: 4-momenta of all other particles (charged
leptons, neutrinos, photons, ...). The
particle_IDs(j)
can be used to select the desired
momentum, as it returns the particle identification code according
to the Monte Carlo particle numbering scheme.
jets(i,j,L)
: array with the jet information
(4-momenta, mass, \(p_T\), rapidity \(y\), azimuthal angle
\(\phi\)).
leptons(i,j,L)
: array with the charged lepton
information (4-momenta, mass, \(p_T\), rapidity \(y\), azimuthal
angle \(\phi\)).
photons(i,j,L)
: array with the photon information
(4-momenta, mass, \(p_T\), rapidity \(y\), azimuthal angle
\(\phi\)).
L
marking the kinematic configurations. It is always a
good practice to print out the value of an unknown variable to get
more information about it.