flag
Vincia:CheckAntennae
(default = on
)mode
Vincia:nPointsCheck
(default = 1000
; minimum = 0
; maximum = 1e6
)parm
Vincia:PacceptFuss
(default = 1.05
; minimum = 1.0
; maximum = 2.0
)parm
Vincia:PacceptPT0
(default = 1.5
; minimum = 0.5
; maximum = 10.0
)flag
Vincia:PrintPacceptVariations
(default = off
)flag
Vincia:PrintReWeightVariations
(default = off
)parm
Vincia:deadZoneAvoidance
(default = 0.0001
; minimum = 0.0
; maximum = 1.0
)Note that the sector shower can not be used in this version of Vincia. In order to use the sector shower shower for the final state in electron-positron annihilation we refer to Vincia version 1.X.
Sector showers are implemented as a non-default option and can be switched on using the flagflag
Vincia:sectorShower
(default = off
)option
off : No sector ordering is imposed. All antennae are
allowed to contribute freely, independently of overlapping
radiation.
option
on : Only one antenna is allowed to contribute to each
phase space point. Note: when this option is on, a set of additional
terms will automatically be added to VINCIA's
antenna functions, such that the entire collinear singularity of
each gluon is present in each antenna.
When the sector option is on, the following switch determines whether the additional gluon-collinear terms are added to the global antenna functions in order to create proper sector antennae from them,
flag
Vincia:useSectorTerms
(default = on
)on
for normal runs. Setting it to off
will
set the additional gluon-collinear sector antenna term coefficients to
zero.
For the time being, only one option for how to distinguish between sectors has been implemented, as follows. A given trial emission will only be accepted if, after the branching, it has the lowest pT (as defined for Type 1 evolution above) of all possible colour-ordered 3→2 clusterings after the branching.
Note that the one-loop matching can not be used in this version of Vincia. In order to use it for Z decay electron-positron annihilation we refer to Vincia version 1.X.
mode
Vincia:matchingNLO
(default = 0
; minimum = 0
; maximum = 2
)2
would invoke one-loop matching
up to and including X+1
partons (one emission plus one
loop gives two powers of alphaS), to the extent the
relevant matrix elements are available in the code, see
the list below. In other words, to include
one-loop matching for X+n
partons, this switch must be
set to n+1
.
The value 0
is equivalent to switching matching off.
Note: values larger than the leading-order value above will be
ignored. Thus, to switch off all matrix-element corrections,
it is sufficient to switch off the LO ones.
The choice of functional form of the renormalisation scale used for the alphaS power associated with the one-loop correction amounts to an NNLO effect and is hence formally beyond the explicit control of the NLO matching. It is controlled by the following parameter:
mode
Vincia:alphaSmodeNLO
(default = 0
; minimum = 0
; maximum = 1
)option
0 : The invariant mass of the parton system, m(ijk).
option
1 : Transverse momentum, defined as in ARIADNE, pT = m(ij)*m(jk)/m(ijk).
0
, has been chosen to limit the absolute size of the NLO corrections, especially for soft branchings. For hard corrections, there should not be much difference between the two choices (though one can of course always argue about factors of 2). For soft corrections, differences appear starting from order aS2*Log(s/pT2). Thus, changing to 1
increases the absolute size of the NLO corrections for soft branchings. Ideally, the shower and hadronisation parameters should then be retuned.
1
is intended mostly for theoretical reference. The matching expression used in the code is of the form (1 + V), which implicitly assumes that the correction, V, is small. For option 1
, however, V becomes large for soft branchings. In this case, a resummed form of the matching expression would have to be used instead, but such an expression has so far not been derived.
mode
Vincia:matchingNLOnPointsMin
(default = 25
; minimum = 10
; maximum = 10000
)mode
Vincia:matchingNLOnPointsMax
(default = 100000
; minimum = 10
; maximum = 1000000
)flag
Vincia:hyperjet
(default = off
)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
.
flag
Vincia:postponeMarkov
(default = off
)