WHIZARD

ISR failed with UFO model

Asked by laetitia

Hi,

I study the process e+e- -> ttbar. I would like to study the beam effect on the production cross section as function of a coefficient from UFO model.
In the UFO model, the electron mass value is not parameterized and Whizard gave an error when I use the ISR effect.
Is it possible to set a mass to electron ?

Whizard gives:

Reading model file '/StageM2/whizard/install/share/whizard/models/SM.mdl'
| Preloaded model: SM
| Process library 'default_lib': initialized
| Preloaded library: default_lib
| Reading model file '/StageM2/whizard/install/share/whizard/models/SM_hadrons.mdl'
| Reading commands from file 'test_beam_365.sin'
| Model: Generating model 'dim6top_LO_UFO' from UFO sources
| Model: Searching for UFO sources in working directory
| Model: Found UFO sources for model 'dim6top_LO_UFO'
| Model: Model file 'dim6top_LO_UFO.ufo.mdl' generated
| Reading model file 'dim6top_LO_UFO.ufo.mdl'
| Switching to model 'dim6top_LO_UFO' (generated from UFO source)
| Process library 'default_lib': recorded process 'bornproc'
sqrts = 3.650000000000E+02
| Process library 'default_lib': compiling ...
| Process library 'default_lib': keeping makefile
| Process library 'default_lib': keeping driver
| Process library 'default_lib': active
| Process library 'default_lib': ... success.
dim6top_LO_UFO.ctW => -2.000000000000E+00
| RNG: Initializing TAO random-number generator
| RNG: Setting seed for random-number generator to 5422
| Initializing integration for process bornproc:
| Beam structure: e-, e+ => isr
| Beam data (collision):
| e- (mass = 0.0000000E+00 GeV)
| e+ (mass = 0.0000000E+00 GeV)
| sqrts = 3.650000000000E+02 GeV
******************************************************************************
******************************************************************************
*** FATAL ERROR: ISR: Particle mass is zero
******************************************************************************
******************************************************************************
WHIZARD run aborted.

My input file :
--------------------------------------------
model=dim6top_LO_UFO (ufo)
beams = "e-", "e+" => isr
process bornproc = "e-", "e+" => "t","t~"
sqrts = 365 GeV
compile
# plot
plot lineshape_born
#scan
scan ctW = ((-2 GeV => 2 GeV /+ 0.3 GeV)){
  integrate (bornproc) { iterations = 2:100000:"gw", 1:100000 }
  record lineshape_born (ctW, integral (bornproc) / 1000 , error (bornproc) / 1000)
}
compile_analysis { $out_file = "ctw_beam_365.dat" }
-------------------------------------------
I used whizard -3.0.2.

Thanks a lot!
Laetitia

Question information

Language:
English Edit question
Status:
Solved
For:
WHIZARD Edit question
Assignee:
Thorsten Ohl Edit question
Solved by:
Juergen Reuter
Solved:
Last query:
Last reply:
Revision history for this message
Thorsten Ohl (thomega) said : 		#1

Hi Laetitia,

in your UFO model, the masses of of the electrons (and muons) is explicitely set to
ZERO in the file particles.py and WHIZARD respects this:

e__minus__ = Particle(pdg_code = 11,
                      name = 'e-',
                      antiname = 'e+',
                      spin = 2,
                      color = 1,
                      mass = Param.ZERO,
                      width = Param.ZERO,
                      texname = 'e-',
                      antitexname = 'e+',
                      charge = -1,
                      GhostNumber = 0,
                      LeptonNumber = 1,
                      Y = 0)

You have to replace "mass = Param.ZERO" by "mass = Param.mass_electron"
and add

mass_electron = Parameter(name = 'mass_electron',
               nature = 'external',
               type = 'real',
               value = 0.000511,
               texname = 'm_e',
               lhablock = 'MASS',
               lhacode = [ 11 ])

to parameters.py.

Revision history for this message
Best Juergen Reuter (j.r.reuter) said : 		#2

Dear Laetitia,
there is actually a much simpler possibility than to edit the UFO file: within your SINDARIN,
set
isr_mass = 511 keV
This will set the electron mass for the electron PDF (resummed ISR radiation) to its physical
value, but in the matrix elements of your hard process, you keep the electron mass zero as
the default in your UFO model.
Cheers,
    JRR (Juergen Reuter)

Revision history for this message
laetitia (laetitia38) said : 		#3

Thanks Juergen Reuter, that solved my question.