The following switches control which quarks and leptons are treated as massive during the perturbative evolution. Note: the values of the masses are in all cases taken from PYTHIA's particle database, minimizing the risk of conflict. The parameters here only control whether the corresponding particles are treated as massive or massless by VINCIA.
flag
Vincia:isMassiveS
(default = false
)flag
Vincia:isMassiveC
(default = true
)flag
Vincia:isMassiveB
(default = true
)flag
Vincia:isMassiveTau
(default = true
)Note: New-physics particles will generally be treated as massive if their masses are larger than the lightest quark for which mass corrections are switched on.
Note 2: For particles that are treated as massive, the mass corrections to the antenna functions are discussed separately, in the section on Antenna Functions.
parm
Vincia:alphaSvalue
(default = 0.139
)mode
Vincia:alphaSorder
(default = 2
; minimum = 0
; maximum = 2
)option
0 : zeroth order, i.e. αs is kept
fixed.
option
1 : first order, i.e., one-loop running.
option
2 : second order, i.e., two-loop running.
All-orders resummation arguments [CMW91] show that a universal next-to-leading correction factor associated with soft gluon emission can be absorbed in coherent parton showers by applying the so-called CMW rescaling to the MSbar value of alphaS. This translation amounts to an nf-dependent rescaling of the value of alphaS, relative to its MSbar value, as follows:
flag
Vincia:alphaScmw
(default = on
)option
on : CMW. This option is recommended for the most accurate shower resummation.
option
off : MSbar.
Note: The CMW arguments were derived using two-loop running.
Note 2: When this correction is switched on, the rescaling of the coupling
away from its MSbar value is properly taken
into account by VINCIA's one-loop matching. When switched off, the
one-loop corrections generally become larger, to compensate for the missing
universal factor.
When Vincia:alphaSorder
is non-zero,
the actual value is regulated by running to the scale
kμ*μR, at which the shower evaluates
αs.
The functional form of μR is given by
Vincia:alphaSmode
and the scale factor
kμ is given by Vincia:alphaSkMu
.
The functional form of μR is given by
mode
Vincia:alphaSmode
(default = 1
; minimum = 0
; maximum = 1
)option
0 : The invariant mass of the mother antenna, m(ijk).
option
1 : For gluon emissions: transverse momentum, defined as in ARIADNE, pT = m(ij)*m(jk)/m(ijk). For gluon splittings, g→qq, the qqbar invariant mass, m(qqbar).
The scale factor kμ is given by
parm
Vincia:alphaSkMu
(default = 1.0
; minimum = 0.1
; maximum = 10.0
)Vincia:alphaSmode
times this
scale factor, i.e., it gives the value of kμ in
the argument to
alphaS(kμ*μR).
parm
Vincia:alphaSmuMin
(default = 0.5
; minimum = 0.1
; maximum = 10.0
)parm
Vincia:alphaSmax
(default = 1.0
; minimum = 0.1
; maximum = 10.0
)