It is possible to pass the parton systems produced by VINCIA
through PYTHIA's string hadronization 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 hadronization
cutoff.
The hadronization cutoff, a.k.a. the infrared regularization 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 hadronization is switched on, there is a delicate interplay between the hadronization scale used in the shower and the parameters of the hadronization model. Ideally, the parameters of the hadronization model should scale as a function of the shower cutoff. This scaling does not happen automatically in current hadronization models, such as the string model employed by PYTHIA. Instead, the parameters of the hadronization model are tuned for one specific shower setting at a time.
mode
Vincia:cutoffType
(default = 1
; minimum = -1
; maximum = 2
)option
-1 :
The cutoff is taken in PYTHIA 8's pTevol
variable (times two, in order to use the same normalization
as in the rest of Vincia). The cutoff scale is then set by the
PYTHIA 8 parameter 2*TimeShower:pTmin
. This is intended as a
first crude way of using Vincia together with PYTHIA 8's
hadronization model without having to retune the latter. Ultimately,
dedicated tunes of the hadronization parameters using VINCIA should
be used instead.
option
0 :
Automatically set cutoffType
equal to
evolutionType
(only applies to infrared sensible
evolution variables)
option
1 : Cutoff in pT (defined as the type 1 evolution
variable, see evolutionType
)
option
2 : Cutoff in dipole virtuality (defined as the
type 2 evolution variable, see evolutionType
)
= -1 |
= 1 |
= 2 |
(cutoff at 2*TimeShower:pTmin ) |
(cutoff at Vincia:cutoffScale ) |
(cutoff at Vincia:cutoffScale ) |
![]() |
![]() |
![]() |
parm
Vincia:cutoffScale
(default = 1.0
)Vincia:cutoffType >= 0
, this parameter sets the
value (in GeV) of the shower cutoff, interpreted according to
the functional form selected under
Vincia:cutoffType
.
Note that all evolution/cutoff
variables are normalized so that their maximum value is equal to the
parent dipole mass. For instance, a type 1 cutoff at QI = 1.0
GeV therefore corresponds to a transverse-momentum cutoff at
pT = 0.5 GeV. See evolutionType
for
further information on the normalization.