Evolution with Biased Kernels

VINCIA's shower evolution can be biased to populate the multi-jet phase space more efficiently and/or enhance the rate of rare processes such as g→bb and g→cc splittings. It is also possible to inhibit radiation (e.g., to focus on Sudakov regions), by choosing biasing factors smaller than unity. When these options are used, it is important to note that the event weights will be modified, reflecting that some types of events (e.g., multijet events, or events with gluon splittings to heavy quarks) will be "overrepresented" statistically, and others (events with few jets, or events with no gluon splittings to heavy quarks) underrepresented. Averages and histograms will therefore only be correct if computed using the correct weight for each generated event. A description and proof of the algorithm can be found in [MS16]. Note that care has been taken to ensure that the weights remain positive definite; under normal circumstances, VINCIA's biasing algorithm should not result in any negative weights.

flag  Vincia:biasInHardProcess   (default = on)
This flag controls whether the biasing factors are applied to shower branchings in the hard-process system.

flag  Vincia:biasInResonanceDecays   (default = on)
This flag controls whether the biasing factors are applied in any resonance-decay systems (like Z/W/H decays) that are not treated as part of the hard process.

flag  Vincia:biasInMPIshowers   (default = off)
This flag controls whether the biasing factors are applied to shower branchings in MPI systems.

parm  Vincia:biasAll   (default = 1.0; minimum = 0.01; maximum = 100.0)
This bias is applied as a multiplicative factor common to all antenna functions, increasing the likelihood of all shower branchings by the same amount and thus more frequently yielding "busy" events, with many shower branchings.

parm  Vincia:biasBottom   (default = 1.0; minimum = 0.01; maximum = 100.0)
This bias enhances the probability for all branchings that increase the number of bottom quarks (i.e., FSR g→bb splittings and the corresponding ISR flavour-excitation process). Note: this factor is applied on top of Vincia:biasAll.

parm  Vincia:biasCharm   (default = 1.0; minimum = 0.01; maximum = 100.0)
Same as Vincia:biasFacBottom but for charm quarks. Note: this factor is applied on top of Vincia:biasAll.

parm  Vincia:biasCutoff   (default = 10.0; minimum = 0.0; maximum = 1000.0)
Do not apply biasing to branchings below this scale. Intended to be used to focus on enhancements of hard branchings only.