Hadronisation

It is possible to pass the parton systems produced by VINCIA through PYTHIA's string hadronisation model. Normally, this should happen automatically, according to the setting of the PYTHIA switch HadronLevel:all. The main parameter from the shower side is then the phase-space contour defined by the hadronisation cutoff.

The hadronisation cutoff, a.k.a. the infrared regularisation scale, defines the resolution scale at which the perturbative shower evolution is stopped. Thus, perturbative emissions below this scale are treated as fundmanentally unresolvable and are in effect inclusively summed over.

Important Note: when hadronisation is switched on, there is a delicate interplay between the hadronisation scale used in the shower and the parameters of the hadronisation model. Ideally, the parameters of the hadronisation model should scale as a function of the shower cutoff. This scaling does not happen automatically in current hadronisation models, such as the string model employed by PYTHIA. Instead, the parameters of the hadronisation model are tuned for one specific shower setting at a time and should be retuned if changes are made to the shower cutoff.

Cutoff Variable

mode  Vincia:cutoffTypeF   (default = 1; minimum = 0; maximum = 2)
This parameter selects the functional form of the infrared shower cutoff (a.k.a. hadronisation cutoff) in the final state shower, which defines the factorisation border between the perturbative and non-perturbative regions. The possible options are:
option 0 : Automatically set cutoffType equal to evolutionType (only applies to infrared sensible final state shower)
option 1 : Cutoff in pT2 = sij * sjk / sijk. Note that the arbitrary normalisation factor which is applied to the corresponding gluon-emission evolution variable is here absent.
option 2 : Cutoff in dipole virtuality mD2 = min(sij,sjk). Note that the arbitrary normalisation factor which is applied to the corresponding gluon-emission evolution variable is here absent.

= 1 = 2
(cutoff at Vincia:cutoffScaleFF) (cutoff at Vincia:cutoffScaleFF)
Type1 Type2

mode  Vincia:cutoffTypeI   (default = 0; minimum = 0; maximum = 0)
This parameter selects the functional form of the infrared shower cutoff (a.k.a. hadronisation cutoff) in the initial state shower. At the moment there is only the following option:
option 0 : Automatically set cutoffType equal to evolutionType (see initial state shower)

Cutoff Scale

parm  Vincia:cutoffScaleFF   (default = 1.15)
This parameter sets the value (in GeV) of the final state shower cutoff, interpreted according to the functional form selected under Vincia:cutoffTypeF.

parm  Vincia:cutoffScaleII   (default = 1.0)
This parameter sets the value (in GeV) of the shower cutoff for initial-initial antennae.

parm  Vincia:cutoffScaleIF   (default = 1.1)
This parameter sets the value (in GeV) of the shower cutoff for initial-final antennae.