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
)
Numerical Parameters
Dead Zone Avoidance Factor
parm
Vincia:deadZoneAvoidance
(default = 0.001
; minimum = 0.0
; maximum = 1.0
)
Antenna functions (in dimensionless form, with the Eikonal
proportional to 2/y1/y2) are not allowed to become smaller than this
number. During initialization of each antenna
function, its finite coefficients will be adjusted, if necessary,
until this condition is satisfied everywhere in phase space.
This is to avoid 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 will be needed
to "make up" for any near-dead zones at the previous branching step.
Shower/Matching Headroom Factor
parm
Vincia:headRoomFactor
(default = 1.5
; minimum = 1.0
; maximum = 10.0
)
A multiplicative factor applied to the trial generator to prevent P >
1 from occurring during trial accept/reject stage. (When matching is
switched off, this factor is set to unity.) Note that, the better the
shower approximation, the smaller this factor can be chosen. The
default value is chosen to work optimally with the ARIADNE kinematics
map. For other kinematics maps, higher settings may be needed to avoid
P > 1 warnings. Note, however, that the code automatically increases
this number (in 10% steps) when P > 1 warnings are encountered, so
such warnings should gradually disappear for long runs, at the expense
of slower running.
Experimental / Development / Advanced Parameters
flag
Vincia:nonRes
(default = off
)
(Experimental flag. Not fully implemented yet. Leave in off position
for physics studies.)
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
.