PHOJET, some important parameters for tuning
Program version 1.05
Most of the program parameters and switches are stored in the common
block /MODELS/. After the initialization call to PHOINP, the
parameters can be changed.
CHARACTER*8 MDLNA
COMMON /MODELS/ MDLNA(50),ISWMDL(50),PARMDL(200),IPAMDL(200)
PHOJET switches
Multiple interactions
- ISWMDL(15)
- multiple soft and hard interaction in non-diffractive events
(default 3)
- 0: only one hard or soft interaction per one event
- 1: only one hard but multiple soft interaction per one event
- 2: only one soft but multiple hard interaction per one event
- 3: multiple soft and hard interactions per one event
- ISWMDL(16)
- multiple soft and hard interaction in diffraction dissociation
(treated as pomeron-particle scattering, default 4)
- 0: only one soft interaction per one event
- 1: only one hard or soft interaction per one event
- 2: only one hard but multiple soft interaction per one event
- 3: only one soft but multiple hard interaction per one event
- 4: multiple soft and hard interactions per one pomeron-particle
scattering
Diffraction dissociation
- ISWMDL(21)
- decay of diffractively produced resonances according to transversally
polarized photons (default 2)
- 0: decay according to phase space
- 1: spin-dependent decay only for low-mass resonances
- 2: spin-dependent decay only for resonances with a mass up to 2 GeV
- ISWMDL(22)
- mass distribution of the diffractively produced system (see manual,
default 1)
- ISWMDL(23)
- simulation of low-mass diffraction (default 1)
- 0: always fragmentation via one string
- 1: superposition of resonances and one-string isotropic background
PHOJET parameters
Soft interaction
The x distributions of low-pt quarks are regularized by a minimum chain mass
cutoff. This cutoff is stored in CUTMU.
COMMON /CUTOFF/ PTCUT(4),CUTMU(4),FPS(4),FPH(4),PSOMIN,XSOMIN
For each interaction type, a separate cutoff can be set (default: 1 GeV).
- CUTMU(1):
chain mass cutoff for scattering of primary particles A and B
- CUTMU(2):
chain mass cutoff for scattering of particle A and pomeron
(diffraction dissociation of particle A)
- CUTMU(3):
chain mass cutoff for scattering of particle B and pomeron
(diffraction dissociation of particle B)
- CUTMU(4):
chain mass cutoff for scattering of pomeron-pomeron scattering
(central diffraction)
Hard interaction
By default, the scales Lambda for alpha_s calculations in hard scattering
are taken from the parton distribution functions. These scales can be modified
changing the the following factors
- PARMDL(110):
multiplication factor
for the scale used in the calculation of the
running coupling constant alpha_s of hard
scattering (defaults: p-p 0.075, gamma-p 0.25, gamma-gamma 1.0)
- PARMDL(104):
multiplication factor for the scale
to determine running coupling constant alpha_s in initial state
evolution (default: 1.0)
- PARMDL(108):
multiplication factor for the scale
to determine scale for PDF calculation (default: 1.0)
The variables PTCUT(1-4) store the transverse momentum cutoff for the
to distinguish between hard and soft interactions.
COMMON /CUTOFF/ PTCUT(4),CUTMU(4),FPS(4),FPH(4),PSOMIN,XSOMIN
By default, an
energy-dependent cutoff is calculated according to the c.m. energy of the
collision. The values stored in PTCUT(1-4) should not be changed by the
user. Instead, the cutoff values can be set using
- PARMDL(36):
cutoff for scattering of primary particles A and B
- PARMDL(37):
cutoff for scattering of particle A and pomeron
(diffraction dissociation of particle A)
- PARMDL(38):
cutoff for scattering of particle B and pomeron
(diffraction dissociation of particle B)
- PARMDL(39):
cutoff for scattering of pomeron-pomeron scattering
(central diffraction)
The virtuality cutoff for initial state radiation (ISR) is stored in
- PARMDL(126):
Q^2 cutoff for ISR in scattering of primary particles A and B
- PARMDL(127):
Q^2 cutoff for ISR in scattering of particle A and pomeron
(diffraction dissociation of particle A)
- PARMDL(128):
Q^2 cutoff for ISR in scattering of particle B and pomeron
(diffraction dissociation of particle B)
- PARMDL(129):
Q^2 cutoff for ISR in scattering of pomeron-pomeron scattering
(central diffraction)
The default value for the ISR cutoff
is the (squared) transverse momentum cutoff.
Diffraction dissociation
The lowest mass sampled in inelastic diffractive processes is given by the
maximum of both the minimum chain mass cut and the particle mass+PARMDL(46).
By default, PARMDL(46) = 0.16 GeV. Note that the 1/M**2
mass distribution is suppressed by threshold effects at low masses.
JETSET parameters
There is no tuned parameter set available, the published comparisons
with data have been done using the JETSET versions 7.3 and 7.4 with
PARJ(42) = 1.0. All other parameters have been kept at their defaults.
Some important JETSET parameters
The defaults given for JETSET Version 7.3
PARJ( 2) strangeness suppression (0.3)
MSTJ(12) popcorn effect (2)
PARJ(19) popcorn (1.0)
PARJ(41) Lund fragmentation function a (0.5)
PARJ(42) Lund fragmentation function b (0.9)
PARJ(21) sigma in soft pt distribution (0.35)
Ralph Engel
March 5, 1997