VINCIA Internal Parameters
Checks and Warnings
Check of antenna functions
By default, Vincia checks antenna functions for positivity and absence
of dead zones.
flag
Vincia:CheckAntennae
(default = on
)
Switch to control whether to perform
antenna self-consistency checks or not.
mode
Vincia:nPointsCheck
(default = 1000
; minimum = 0
; maximum = 1e6
)
Number of random points to check each antenna functions for positivity.
Numerical Parameters
Dead Zone Avoidance Factor
parm
Vincia:deadZoneAvoidance
(default = 0.0001
; minimum = 0.0
; maximum = 1.0
)
During initialization, warnings are issued if any
antenna functions (in dimensionless form, with the Eikonal
proportional to 2/y1/y2) become smaller than this number, anywhere in the resolved part of phase space (away from phase-space boundaries).
This is to warn against spurious radiation zeroes or large
negative finite terms creating "dead zones", or near-dead zones,
in the shower. For LL showering and matching up to
NLO, there is in principle no problem in taking this parameter to zero if
so desired. However, for the NLL and higher-order matching
corrections, very small values of this parameter may result in weights
greater than unity being generated, since the corrections are
multiplicative and large reweighting factors may be needed
to "make up" for any near-dead zones at the previous branching step.
NLO DeltaA Evaluation
mode
Vincia:matchingNLOnPointsMin
(default = 100
; minimum = 10
; maximum = 10000
)
Minimal number of MC points used for the numerical evaluation of the real-emission correction integrals (deltaA) terms when computing NLO matching coefficients. Note that all possible forward branchings are cycled through, so e.g. for Z to 3 jets, four 4-parton matrix elements (2 qggq and 2 qqqq ones)
are tested for each MC point.
Experimental / Development / Advanced Parameters
flag
Vincia:hyperjet
(default = off
)
(Experimental flag. Not fully implemented yet. Leave in off position
for physics studies.)
When this flag is switched on
, VINCIA will automatically
use modified gluon emission antenna functions, in which the Eikonal (soft)
terms have been subtracted out, for the showers off the hardest
interaction. The gluon splitting antennae and the gluon emission
antennae for radiation inside resonance decays (and for showers off
MPI) are left
unmodified. Since the modified gluon emission antennae no longer contain
a soft singularity, this will NOT generate the correct DGLAP evolution
if used together with normal matrix elements for the hard
process. This option is therefore only intended for use together with
matrix element events in which the soft Eikonal has already been
resummed, such as when VINCIA is used together with J. Andersen's
high-energy-limit matrix elements. Since these matrix element
expressions are correct in the high-y-per-jet limit,
we have dubbed this running mode HyperJet
.