VINCIA Internal Parameters

Verbose Level

mode  Vincia:verbose   (default = 1; minimum = 0; maximum = 9)
Level of detail of information written to standard output on what goes on inside VINCIA. Settings different from zero and one are intended for debugging purposes and hence should not be used for normal runs.

option 0 : No runtime output.



Note: options 1-3 only generate output when something goes wrong, i.e., a check fails, etc.

option 1 : Normal runtime output. Warnings and errors are printed, but no additional diagnostic output is given.
option 2 : Enhanced runtime output. As for =1, but limited additional diagnostic info is given. Also, internal VINCIA diagnostics histograms are booked and filled, especially for matching. These can be printed by the user at any time (e.g., after a run) using the VinciaPlugin::printHistos() method.
option 3 : As for =2, but as much diagnostic output as possible is given for each error or warning. Also, a consistency check is added to each branching by reclustering the resulting momenta back using the corresponding inverse kinematics map and checking that the original momenta are recovered within the desired numerical precision.


Note: options above 4 will always generate output for each event, so will cause very large amounts of output.

option 4 : As for =3. And: each prepare() and pTnext() call is explicitly announced, with system number and restart scale printed out, respectively. .
option 5 : As for =4. And: momentum listings are printed for each configuration that violates P < 1.
option 6 : As for =5. And: each main function call is explicitly announced with begin and end printed to output.
option 7 : As for =6. And: most function calls are explicitly announced with begin and end printed to output (still only partly implemented).
option 8 : As for =7. And: last semi-sensible level of output.
option 9 : As for =8. And: all possible output.

Numerical Parameters

Warning: do not change these parameters unless you have a very good reason to do so.

Dead Zone Avoidance Factor

parm  Vincia:deadZoneAvoidance   (default = 0.01; minimum = 0.0; maximum = 2.0)
In the shower, the finite terms of each antenna function are not allowed to cause the full antenna function (expressed in dimensionless quantities) to become smaller than this number. During initialization of each antenna function, its C00 coefficient 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.

Maximum Uncertainty Deviation

In the uncertainty band evaluation, the maximum deviation allowed for each branching variation, relative to the user settings, is constrained by

parm  Vincia:uncertaintyBandsMaxDev   (default = 2.0; minimum = 1.0; maximum = 10.0)
Maximum allowed value for the ratio of an uncertainty variation to the nominal (user) branching probability, for each branching. Should normally be left in its default position, unless you are an experienced user and know what you're doing. Note: this works in both directions, i.e., the relative branching probability is forced to be in the range

1 / Vincia:uncertaintyBandsMaxDev < P'/P < Vincia:uncertaintyBandsMaxDev

where P' is the branching probability according to the variation, and P is the probability with the settings chosen by the user. Note also that the total shower weight is built up by products of many branchings, so that the final answer may differ by more than Vincia:uncertaintyBandsMaxDev.

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.

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