Bhabha scattering and multilepton processes

Asked by Gabriele Martelli on 2020-04-10

Hello!! I'm trying to generate e+ e- > n(e+ e-) processes, where n goes from1 to 3, at low energy (positron beam = 550 MeV) and with the electron target at rest.
The first process I was trying to simulate is the Bhabha scattering. In order to do so, I changed the EM coupling constant from 1/128 to 1/137 'cause I want only the photon as a mediator boson. After that, I generated the process, with a 50 MeV cut on the minimun energy of the final leptons in order to prevent the cross section from diverging, but the generation failed.

Since the first failure, some questions have occurred to me and I hope to find the answers with you:

1) After many tries I saw that if I put a cut on the traverse momentum the generations will not fail but I will obtain false cross sections (I have CalcHEP cross section values for comparison). Is the cut on the transverse momentum mandatory on Madgraph? Is there a way to put it to zero and obtain a real value of cross section?

2) When I generate a process on CalcHEP, if it is complicate it will take some time to obtain a real value. It will show you some fake values and then the real one.
I tried the e+ e- > 2(e+e-) on CalcHEP and after some trials I obtained the expected value of cross section. On Madgraph (using again an apparently mandatory cut on the pt) I obtained, as a final cross section value, one of the fake value than CalcHEP has discarded. How is it possible?

3) CalcHEP is unable to generate process with 6 leptons in the final state? Is Madgraph capable to do it?

To help you better understand my problems, I paste here my param_card and my run_ card from the Bhabha process(note that I use the model sm).

PARAM_CARD

######################################################################
## PARAM_CARD AUTOMATICALY GENERATED BY MG5 FOLLOWING UFO MODEL ####
######################################################################
## ##
## Width set on Auto will be computed following the information ##
## present in the decay.py files of the model. ##
## See arXiv:1402.1178 for more details. ##
## ##
######################################################################

###################################
## INFORMATION FOR MASS
###################################
Block mass
    4 1.270000e+00 # MC
    5 4.700000e+00 # MB
    6 1.720000e+02 # MT
   11 5.110000e-04 # Me
   13 1.056600e-01 # MM
   15 1.777000e+00 # MTA
   23 9.118800e+01 # MZ
   25 1.250000e+02 # MH
## Dependent parameters, given by model restrictions.
## Those values should be edited following the
## analytical expression. MG5 ignores those values
## but they are important for interfacing the output of MG5
## to external program such as Pythia.
  1 0.000000e+00 # d : 0.0
  2 0.000000e+00 # u : 0.0
  3 0.000000e+00 # s : 0.0
  12 0.000000e+00 # ve : 0.0
  14 0.000000e+00 # vm : 0.0
  16 0.000000e+00 # vt : 0.0
  21 0.000000e+00 # g : 0.0
  22 0.000000e+00 # a : 0.0
  24 8.093557e+01 # w+ : cmath.sqrt(MZ__exp__2/2. + cmath.sqrt(MZ__exp__4/4. - (aEW*cmath.pi*MZ__exp__2)/(Gf*sqrt__2)))

###################################
## INFORMATION FOR SMINPUTS
###################################
Block sminputs
    1 1.370000e+02 # aEWM1
    2 1.166390e-05 # Gf
    3 1.180000e-01 # aS

###################################
## INFORMATION FOR WOLFENSTEIN
###################################
Block wolfenstein
    1 2.253000e-01 # lamWS
    2 8.080000e-01 # AWS
    3 1.320000e-01 # rhoWS
    4 3.410000e-01 # etaWS

###################################
## INFORMATION FOR YUKAWA
###################################
Block yukawa
    4 1.270000e+00 # ymc
    5 4.200000e+00 # ymb
    6 1.645000e+02 # ymt
   11 5.110000e-04 # yme
   13 1.056600e-01 # ymm
   15 1.777000e+00 # ymtau

###################################
## INFORMATION FOR DECAY
###################################
DECAY 6 1.508336e+00 # WT
DECAY 15 2.270000e-12 # WTau
DECAY 23 2.441404e+00 # WZ
DECAY 24 2.047600e+00 # WW
DECAY 25 6.382339e-03 # WH
## Dependent parameters, given by model restrictions.
## Those values should be edited following the
## analytical expression. MG5 ignores those values
## but they are important for interfacing the output of MG5
## to external program such as Pythia.
DECAY 1 0.000000e+00 # d : 0.0
DECAY 2 0.000000e+00 # u : 0.0
DECAY 3 0.000000e+00 # s : 0.0
DECAY 4 0.000000e+00 # c : 0.0
DECAY 5 0.000000e+00 # b : 0.0
DECAY 11 0.000000e+00 # e- : 0.0
DECAY 12 0.000000e+00 # ve : 0.0
DECAY 13 0.000000e+00 # mu- : 0.0
DECAY 14 0.000000e+00 # vm : 0.0
DECAY 16 0.000000e+00 # vt : 0.0
DECAY 21 0.000000e+00 # g : 0.0
DECAY 22 0.000000e+00 # a : 0.0

RUN_CARD

#*********************************************************************
# MadGraph5_aMC@NLO *
# *
# run_card.dat MadEvent *
# *
# This file is used to set the parameters of the run. *
# *
# Some notation/conventions: *
# *
# Lines starting with a '# ' are info or comments *
# *
# mind the format: value = variable ! comment *
# *
# To display more options, you can type the command: *
# update full_run_card *
#*********************************************************************
#
#*********************************************************************
# Tag name for the run (one word) *
#*********************************************************************
  tag_1 = run_tag ! name of the run
#*********************************************************************
# Number of events and rnd seed *
# Warning: Do not generate more than 1M events in a single run *
#*********************************************************************
  10000 = nevents ! Number of unweighted events requested
  0 = iseed ! rnd seed (0=assigned automatically=default))
#*********************************************************************
# Collider type and energy *
# lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
# 3=photon from electron *
#*********************************************************************
  0 = lpp1 ! beam 1 type
  0 = lpp2 ! beam 2 type
  0.55 = ebeam1 ! beam 1 total energy in GeV
  0 = ebeam2 ! beam 2 total energy in GeV
#*********************************************************************
# Beam polarization from -100 (left-handed) to 100 (right-handed) *
#*********************************************************************
  0.0 = polbeam1 ! beam polarization for beam 1
  0.0 = polbeam2 ! beam polarization for beam 2

#*********************************************************************
# PDF CHOICE: this automatically fixes also alpha_s and its evol. *
#*********************************************************************
  nn23lo1 = pdlabel ! PDF set
  230000 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
# To see heavy ion options: type "update ion_pdf"
#*********************************************************************
# Renormalization and factorization scales *
#*********************************************************************
  False = fixed_ren_scale ! if .true. use fixed ren scale
  False = fixed_fac_scale ! if .true. use fixed fac scale
  91.188 = scale ! fixed ren scale
  91.188 = dsqrt_q2fact1 ! fixed fact scale for pdf1
  91.188 = dsqrt_q2fact2 ! fixed fact scale for pdf2
  -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
  1.0 = scalefact ! scale factor for event-by-event scales
#*********************************************************************
# Type and output format
#*********************************************************************
  False = gridpack !True = setting up the grid pack
  -1.0 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
  average = event_norm ! average/sum. Normalization of the weight in the LHEF
# To see MLM/CKKW merging options: type "update MLM" or "update CKKW"

#*********************************************************************
#
#*********************************************************************
# handling of the helicities:
# 0: sum over all helicities
# 1: importance sampling over helicities
#*********************************************************************
  0 = nhel ! using helicities importance sampling or not.
#*********************************************************************
# Generation bias, check the wiki page below for more information: *
# 'cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOEventGenerationBias' *
#*********************************************************************
  None = bias_module ! Bias type of bias, [None, ptj_bias, -custom_folder-]
  {} = bias_parameters ! Specifies the parameters of the module.
#
#*******************************
# Parton level cuts definition *
#*******************************
#
#
#*********************************************************************
# BW cutoff (M+/-bwcutoff*Gamma) ! Define on/off-shell for "$" and decay
#*********************************************************************
  15.0 = bwcutoff ! (M+/-bwcutoff*Gamma)
#*********************************************************************
# Standard Cuts *
#*********************************************************************
# Minimum and maximum pt's (for max, -1 means no cut) *
#*********************************************************************
  0.0 = ptl ! minimum pt for the charged leptons
  -1.0 = ptlmax ! maximum pt for the charged leptons
  {} = pt_min_pdg ! pt cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = pt_max_pdg ! pt cut for other particles (syntax e.g. {6: 100, 25: 50})
#*********************************************************************
# Minimum and maximum E's (in the center of mass frame) *
#*********************************************************************
  0.0 = ej ! minimum E for the jets
  0.0 = eb ! minimum E for the b
  0.0 = ea ! minimum E for the photons
  0.05 = el ! minimum E for the charged leptons
  -1.0 = ejmax ! maximum E for the jets
  -1.0 = ebmax ! maximum E for the b
  -1.0 = eamax ! maximum E for the photons
  -1.0 = elmax ! maximum E for the charged leptons
  {} = e_min_pdg ! E cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = e_max_pdg ! E cut for other particles (syntax e.g. {6: 100, 25: 50})

#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  -1.0 = etal ! max rap for the charged leptons
  0.0 = etalmin ! main rap for the charged leptons
  {} = eta_min_pdg ! rap cut for other particles (use pdg code). Applied on particle and anti-particle
  {} = eta_max_pdg ! rap cut for other particles (syntax e.g. {6: 2.5, 23: 5})
#*********************************************************************
# Minimum and maximum DeltaR distance *
#*********************************************************************
  0.0 = drll ! min distance between leptons
  -1.0 = drllmax ! max distance between leptons
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
#*********************************************************************
  0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
  -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
  {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
  {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
                       ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
 #*********************************************************************
 # Minimum and maximum invariant mass for all letpons *
 #*********************************************************************
  0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
  -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
 #*********************************************************************
 # Minimum and maximum pt for 4-momenta sum of leptons *
 #*********************************************************************
  0.0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
  -1.0 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
  0.0 = xptl ! minimum pt for at least one charged lepton
 #*********************************************************************
 # Control the pt's of leptons sorted by pt *
 #*********************************************************************
  0.0 = ptl1min ! minimum pt for the leading lepton in pt
  0.0 = ptl2min ! minimum pt for the second lepton in pt
  -1.0 = ptl1max ! maximum pt for the leading lepton in pt
  -1.0 = ptl2max ! maximum pt for the second lepton in pt
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
  4 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: Do not use for interference type of computation *
#*********************************************************************
  False = use_syst ! Enable systematics studies
#
  systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
# Syscalc is deprecated but to see the associate options type'update syscalc'#*********************************************************************
# Additional hidden parameters
#*********************************************************************
  ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments # Choose the argment to pass to the systematics command. like --mur=0.25,1,4. Look at the help of the systematics function for more details.

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
2020-04-11
Last reply:
2020-04-11

Hi,

- Did you notice that the energy cut was applied in the center of mass frame?
I guess that you have to adapt your cut accordingly.

They are no mandatory cut so you do not need to put a pt cut.

> Madgraph (using again an apparently mandatory cut on the pt) I obtained, as a final cross section value, one of the fake value than CalcHEP has discarded. How is it possible?

Just bad luck I guess...

> 3) CalcHEP is unable to generate process with 6 leptons in the final state? Is Madgraph capable to do it?

Yes we can

Cheers,

Olivier

> On 10 Apr 2020, at 16:52, Gabriele Martelli <email address hidden> wrote:
>
> New question #689819 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/689819
>
> Hello!! I'm trying to generate e+ e- > n(e+ e-) processes, where n goes from1 to 3, at low energy (positron beam = 550 MeV) and with the electron target at rest.
> The first process I was trying to simulate is the Bhabha scattering. In order to do so, I changed the EM coupling constant from 1/128 to 1/137 'cause I want only the photon as a mediator boson. After that, I generated the process, with a 50 MeV cut on the minimun energy of the final leptons in order to prevent the cross section from diverging, but the generation failed.
>
> Since the first failure, some questions have occurred to me and I hope to find the answers with you:
>
> 1) After many tries I saw that if I put a cut on the traverse momentum the generations will not fail but I will obtain false cross sections (I have CalcHEP cross section values for comparison). Is the cut on the transverse momentum mandatory on Madgraph? Is there a way to put it to zero and obtain a real value of cross section?
>
> 2) When I generate a process on CalcHEP, if it is complicate it will take some time to obtain a real value. It will show you some fake values and then the real one.
> I tried the e+ e- > 2(e+e-) on CalcHEP and after some trials I obtained the expected value of cross section. On Madgraph (using again an apparently mandatory cut on the pt) I obtained, as a final cross section value, one of the fake value than CalcHEP has discarded. How is it possible?
>
> 3) CalcHEP is unable to generate process with 6 leptons in the final state? Is Madgraph capable to do it?
>
> To help you better understand my problems, I paste here my param_card and my run_ card from the Bhabha process(note that I use the model sm).
>
> PARAM_CARD
>
> ######################################################################
> ## PARAM_CARD AUTOMATICALY GENERATED BY MG5 FOLLOWING UFO MODEL ####
> ######################################################################
> ## ##
> ## Width set on Auto will be computed following the information ##
> ## present in the decay.py files of the model. ##
> ## See arXiv:1402.1178 for more details. ##
> ## ##
> ######################################################################
>
> ###################################
> ## INFORMATION FOR MASS
> ###################################
> Block mass
> 4 1.270000e+00 # MC
> 5 4.700000e+00 # MB
> 6 1.720000e+02 # MT
> 11 5.110000e-04 # Me
> 13 1.056600e-01 # MM
> 15 1.777000e+00 # MTA
> 23 9.118800e+01 # MZ
> 25 1.250000e+02 # MH
> ## Dependent parameters, given by model restrictions.
> ## Those values should be edited following the
> ## analytical expression. MG5 ignores those values
> ## but they are important for interfacing the output of MG5
> ## to external program such as Pythia.
> 1 0.000000e+00 # d : 0.0
> 2 0.000000e+00 # u : 0.0
> 3 0.000000e+00 # s : 0.0
> 12 0.000000e+00 # ve : 0.0
> 14 0.000000e+00 # vm : 0.0
> 16 0.000000e+00 # vt : 0.0
> 21 0.000000e+00 # g : 0.0
> 22 0.000000e+00 # a : 0.0
> 24 8.093557e+01 # w+ : cmath.sqrt(MZ__exp__2/2. + cmath.sqrt(MZ__exp__4/4. - (aEW*cmath.pi*MZ__exp__2)/(Gf*sqrt__2)))
>
> ###################################
> ## INFORMATION FOR SMINPUTS
> ###################################
> Block sminputs
> 1 1.370000e+02 # aEWM1
> 2 1.166390e-05 # Gf
> 3 1.180000e-01 # aS
>
> ###################################
> ## INFORMATION FOR WOLFENSTEIN
> ###################################
> Block wolfenstein
> 1 2.253000e-01 # lamWS
> 2 8.080000e-01 # AWS
> 3 1.320000e-01 # rhoWS
> 4 3.410000e-01 # etaWS
>
> ###################################
> ## INFORMATION FOR YUKAWA
> ###################################
> Block yukawa
> 4 1.270000e+00 # ymc
> 5 4.200000e+00 # ymb
> 6 1.645000e+02 # ymt
> 11 5.110000e-04 # yme
> 13 1.056600e-01 # ymm
> 15 1.777000e+00 # ymtau
>
> ###################################
> ## INFORMATION FOR DECAY
> ###################################
> DECAY 6 1.508336e+00 # WT
> DECAY 15 2.270000e-12 # WTau
> DECAY 23 2.441404e+00 # WZ
> DECAY 24 2.047600e+00 # WW
> DECAY 25 6.382339e-03 # WH
> ## Dependent parameters, given by model restrictions.
> ## Those values should be edited following the
> ## analytical expression. MG5 ignores those values
> ## but they are important for interfacing the output of MG5
> ## to external program such as Pythia.
> DECAY 1 0.000000e+00 # d : 0.0
> DECAY 2 0.000000e+00 # u : 0.0
> DECAY 3 0.000000e+00 # s : 0.0
> DECAY 4 0.000000e+00 # c : 0.0
> DECAY 5 0.000000e+00 # b : 0.0
> DECAY 11 0.000000e+00 # e- : 0.0
> DECAY 12 0.000000e+00 # ve : 0.0
> DECAY 13 0.000000e+00 # mu- : 0.0
> DECAY 14 0.000000e+00 # vm : 0.0
> DECAY 16 0.000000e+00 # vt : 0.0
> DECAY 21 0.000000e+00 # g : 0.0
> DECAY 22 0.000000e+00 # a : 0.0
>
>
> RUN_CARD
>
> #*********************************************************************
> # MadGraph5_aMC@NLO *
> # *
> # run_card.dat MadEvent *
> # *
> # This file is used to set the parameters of the run. *
> # *
> # Some notation/conventions: *
> # *
> # Lines starting with a '# ' are info or comments *
> # *
> # mind the format: value = variable ! comment *
> # *
> # To display more options, you can type the command: *
> # update full_run_card *
> #*********************************************************************
> #
> #*********************************************************************
> # Tag name for the run (one word) *
> #*********************************************************************
> tag_1 = run_tag ! name of the run
> #*********************************************************************
> # Number of events and rnd seed *
> # Warning: Do not generate more than 1M events in a single run *
> #*********************************************************************
> 10000 = nevents ! Number of unweighted events requested
> 0 = iseed ! rnd seed (0=assigned automatically=default))
> #*********************************************************************
> # Collider type and energy *
> # lpp: 0=No PDF, 1=proton, -1=antiproton, 2=photon from proton, *
> # 3=photon from electron *
> #*********************************************************************
> 0 = lpp1 ! beam 1 type
> 0 = lpp2 ! beam 2 type
> 0.55 = ebeam1 ! beam 1 total energy in GeV
> 0 = ebeam2 ! beam 2 total energy in GeV
> #*********************************************************************
> # Beam polarization from -100 (left-handed) to 100 (right-handed) *
> #*********************************************************************
> 0.0 = polbeam1 ! beam polarization for beam 1
> 0.0 = polbeam2 ! beam polarization for beam 2
>
>
> #*********************************************************************
> # PDF CHOICE: this automatically fixes also alpha_s and its evol. *
> #*********************************************************************
> nn23lo1 = pdlabel ! PDF set
> 230000 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
> # To see heavy ion options: type "update ion_pdf"
> #*********************************************************************
> # Renormalization and factorization scales *
> #*********************************************************************
> False = fixed_ren_scale ! if .true. use fixed ren scale
> False = fixed_fac_scale ! if .true. use fixed fac scale
> 91.188 = scale ! fixed ren scale
> 91.188 = dsqrt_q2fact1 ! fixed fact scale for pdf1
> 91.188 = dsqrt_q2fact2 ! fixed fact scale for pdf2
> -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
> 1.0 = scalefact ! scale factor for event-by-event scales
> #*********************************************************************
> # Type and output format
> #*********************************************************************
> False = gridpack !True = setting up the grid pack
> -1.0 = time_of_flight ! threshold (in mm) below which the invariant livetime is not written (-1 means not written)
> average = event_norm ! average/sum. Normalization of the weight in the LHEF
> # To see MLM/CKKW merging options: type "update MLM" or "update CKKW"
>
> #*********************************************************************
> #
> #*********************************************************************
> # handling of the helicities:
> # 0: sum over all helicities
> # 1: importance sampling over helicities
> #*********************************************************************
> 0 = nhel ! using helicities importance sampling or not.
> #*********************************************************************
> # Generation bias, check the wiki page below for more information: *
> # 'cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LOEventGenerationBias' *
> #*********************************************************************
> None = bias_module ! Bias type of bias, [None, ptj_bias, -custom_folder-]
> {} = bias_parameters ! Specifies the parameters of the module.
> #
> #*******************************
> # Parton level cuts definition *
> #*******************************
> #
> #
> #*********************************************************************
> # BW cutoff (M+/-bwcutoff*Gamma) ! Define on/off-shell for "$" and decay
> #*********************************************************************
> 15.0 = bwcutoff ! (M+/-bwcutoff*Gamma)
> #*********************************************************************
> # Standard Cuts *
> #*********************************************************************
> # Minimum and maximum pt's (for max, -1 means no cut) *
> #*********************************************************************
> 0.0 = ptl ! minimum pt for the charged leptons
> -1.0 = ptlmax ! maximum pt for the charged leptons
> {} = pt_min_pdg ! pt cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = pt_max_pdg ! pt cut for other particles (syntax e.g. {6: 100, 25: 50})
> #*********************************************************************
> # Minimum and maximum E's (in the center of mass frame) *
> #*********************************************************************
> 0.0 = ej ! minimum E for the jets
> 0.0 = eb ! minimum E for the b
> 0.0 = ea ! minimum E for the photons
> 0.05 = el ! minimum E for the charged leptons
> -1.0 = ejmax ! maximum E for the jets
> -1.0 = ebmax ! maximum E for the b
> -1.0 = eamax ! maximum E for the photons
> -1.0 = elmax ! maximum E for the charged leptons
> {} = e_min_pdg ! E cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = e_max_pdg ! E cut for other particles (syntax e.g. {6: 100, 25: 50})
>
> #*********************************************************************
> # Maximum and minimum absolute rapidity (for max, -1 means no cut) *
> #*********************************************************************
> -1.0 = etal ! max rap for the charged leptons
> 0.0 = etalmin ! main rap for the charged leptons
> {} = eta_min_pdg ! rap cut for other particles (use pdg code). Applied on particle and anti-particle
> {} = eta_max_pdg ! rap cut for other particles (syntax e.g. {6: 2.5, 23: 5})
> #*********************************************************************
> # Minimum and maximum DeltaR distance *
> #*********************************************************************
> 0.0 = drll ! min distance between leptons
> -1.0 = drllmax ! max distance between leptons
> #*********************************************************************
> # Minimum and maximum invariant mass for pairs *
> #*********************************************************************
> 0.0 = mmll ! min invariant mass of l+l- (same flavour) lepton pair
> -1.0 = mmllmax ! max invariant mass of l+l- (same flavour) lepton pair
> {} = mxx_min_pdg ! min invariant mass of a pair of particles X/X~ (e.g. {6:250})
> {'default': False} = mxx_only_part_antipart ! if True the invariant mass is applied only
> ! to pairs of particle/antiparticle and not to pairs of the same pdg codes.
> #*********************************************************************
> # Minimum and maximum invariant mass for all letpons *
> #*********************************************************************
> 0.0 = mmnl ! min invariant mass for all letpons (l+- and vl)
> -1.0 = mmnlmax ! max invariant mass for all letpons (l+- and vl)
> #*********************************************************************
> # Minimum and maximum pt for 4-momenta sum of leptons *
> #*********************************************************************
> 0.0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)
> -1.0 = ptllmax ! Maximum pt for 4-momenta sum of leptons(l and vl)
> #*********************************************************************
> # Inclusive cuts *
> #*********************************************************************
> 0.0 = xptl ! minimum pt for at least one charged lepton
> #*********************************************************************
> # Control the pt's of leptons sorted by pt *
> #*********************************************************************
> 0.0 = ptl1min ! minimum pt for the leading lepton in pt
> 0.0 = ptl2min ! minimum pt for the second lepton in pt
> -1.0 = ptl1max ! maximum pt for the leading lepton in pt
> -1.0 = ptl2max ! maximum pt for the second lepton in pt
> #*********************************************************************
> # maximal pdg code for quark to be considered as a light jet *
> # (otherwise b cuts are applied) *
> #*********************************************************************
> 4 = maxjetflavor ! Maximum jet pdg code
> #*********************************************************************
> #
> #*********************************************************************
> # Store info for systematics studies *
> # WARNING: Do not use for interference type of computation *
> #*********************************************************************
> False = use_syst ! Enable systematics studies
> #
> systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
> ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
> # Syscalc is deprecated but to see the associate options type'update syscalc'#*********************************************************************
> # Additional hidden parameters
> #*********************************************************************
> ['--mur=0.5,1,2', '--muf=0.5,1,2', '--pdf=errorset'] = systematics_arguments # Choose the argment to pass to the systematics command. like --mur=0.25,1,4. Look at the help of the systematics function for more details.
>
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Gabriele Martelli (gabmarte) said : #2

Hello Mr Mattaelaer!!

1) I didn't notice that the energy cut was applied in the center of mass frame, my mistake. I have to apply this cut only on the energy of the final state leptons. I am still a novice in using Madgraph, do you have any suggestion on how to implement such cut?

2) I'm sorry but I don't understand how this can be bad luck. I give you another example: I have a theoretical value of the e+e- -> 2(e+e-) cross section without cuts. When I compute this process in CalcHEP, I obtain (after many evaluations in the same run) the expected value. On Madgraph, even if I compute this process many times, I will still obtain the same fake value, as a final result, that can be seen during the CalcHEP computation.
To make the idea clear I show you some numbers:

expected value: 1.29948E+08 pb

CalcHEP value: 1.290934E+08 pb

Madgraph value: 2.68829660329e+11 pb

Cheers,

Gabriele Martelli

Hi,

> 1) I didn't notice that the energy cut was applied in the center of mass
> frame, my mistake. I have to apply this cut only on the energy of the
> final state leptons. I am still a novice in using Madgraph, do you have
> any suggestion on how to implement such cut?

My advise would be then to write in the run_card the minimum energy possible in that frame.
(in principle you can put 0 but I will try to avoid it if possible)

Then you will have to implement your own cut (in fortran) by editing the file
SubProcesses/dummy_functions.f

> 2) I'm sorry but I don't understand how this can be bad luck.

I do not think that the fact that you see the same value within Calchep and madgraph has any meaning that's it.
> expected value: 1.29948E+08 pb
>
> CalcHEP value: 1.290934E+08 pb
>
> Madgraph value: 2.68829660329e+11 pb

This probably just means that you do not have the correct cut setup in madgraph (which would not suprise me due to the first point above)

Cheers,

Olivier

> On 11 Apr 2020, at 14:09, Gabriele Martelli <email address hidden> wrote:
>
> Question #689819 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/689819
>
> Status: Answered => Open
>
> Gabriele Martelli is still having a problem:
> Hello Mr Mattaelaer!!
>
> 1) I didn't notice that the energy cut was applied in the center of mass
> frame, my mistake. I have to apply this cut only on the energy of the
> final state leptons. I am still a novice in using Madgraph, do you have
> any suggestion on how to implement such cut?
>
> 2) I'm sorry but I don't understand how this can be bad luck. I give you another example: I have a theoretical value of the e+e- -> 2(e+e-) cross section without cuts. When I compute this process in CalcHEP, I obtain (after many evaluations in the same run) the expected value. On Madgraph, even if I compute this process many times, I will still obtain the same fake value, as a final result, that can be seen during the CalcHEP computation.
> To make the idea clear I show you some numbers:
>
> expected value: 1.29948E+08 pb
>
> CalcHEP value: 1.290934E+08 pb
>
> Madgraph value: 2.68829660329e+11 pb
>
> Cheers,
>
> Gabriele Martelli
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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