MadGraph5_aMC@NLO

Different results for NLO QCD fixed order cross sections computed with v2.6.5 and v3.0.0

Asked by Pia Bredt

Dear MG5 Team,

As computing NLO QCD cross sections for pp -> Zj with the following statements in the prompt

MG5_aMC>import model loop_sm-no_b_mass
MG5_aMC>set complex_mass_scheme
MG5_aMC>generate p p > z j QCD=1 QED=1 [QCD]

specifying fixed order NLO QCD and using the run_card and param_card as stated below I strangely observed two different results computed with 2 different versions with MadGraph. The first one, computed with v2.6.5 gives

9.74516437e+03 +- 3.1785e+01 pb

With v3.0.0 (using exactly the same prompt statements and run_card and param_card) I get

9.96661952e+03 +- 2.3958e+01 pb

which is about 5.6 sigma off compared to the one computed with the older version. The following warnings came up due to the usage of an older run_card/param_card

INFO: Update the dependent parameter of the param_card.dat
WARNING: Unknow type of information in the card: yukawa
run_card missed argument pt_min_pdg. Takes default: {}
run_card missed argument pt_max_pdg. Takes default: {}
run_card missed argument mxx_min_pdg. Takes default: {}
INFO: Starting run
INFO: Compiling the code
run_card missed argument pt_min_pdg. Takes default: {}
run_card missed argument pt_max_pdg. Takes default: {}
run_card missed argument mxx_min_pdg. Takes default: {}
run_card missed argument shower_scale_factor. Takes default: 1.0
run_card missed argument muf_ref_fixed. Takes default: 91.188
run_card missed argument dynamical_scale_choice. Takes default: [-1]
run_card missed argument muf_over_ref. Takes default: 1.0
run_card missed argument rw_rscale. Takes default: [1.0, 2.0, 0.5]
run_card missed argument rw_fscale. Takes default: [1.0, 2.0, 0.5]
run_card missed argument store_rwgt_info. Takes default: False
run_card missed argument gamma_is_j. Takes default: True
run_card missed argument drll_sf. Takes default: 0.0
run_card missed argument mll_sf. Takes default: 30.0
run_card missed argument rphreco. Takes default: 0.1
run_card missed argument etaphreco. Takes default: -1.0
run_card missed argument lepphreco. Takes default: True
run_card missed argument quarkphreco. Takes default: True
run_card missed argument iappl. Takes default: 0

which should not influence the result actually (or does it?). Can you help which might have happen wrong here by switching the versions of MG5? Any statement which I could have missed?

Thanks in advance and best regards,
Pia

#***********************************************************************
# MadGraph5_aMC@NLO *
# *
# run_card.dat aMC@NLO *
# *
# This file is used to set the parameters of the run. *
# *
# Some notation/conventions: *
# *
# Lines starting with a hash (#) are info or comments *
# *
# mind the format: value = variable ! comment *
#***********************************************************************
#
#*******************
# Running parameters
#*******************
#
#***********************************************************************
# Tag name for the run (one word) *
#***********************************************************************
  tag_1 = run_tag ! name of the run
#***********************************************************************
# Number of events (and their normalization) and the required *
# (relative) accuracy on the Xsec. *
# These values are ignored for fixed order runs *
#***********************************************************************
 10000 = nevents ! Number of unweighted events requested
    -1 = req_acc ! Required accuracy (-1=auto determined from nevents)
    -1 = nevt_job! Max number of events per job in event generation.
                 ! (-1= no split).
average = event_norm ! Normalize events to sum or average to the X sect.
#***********************************************************************
# Number of points per itegration channel (ignored for aMC@NLO runs) *
#***********************************************************************
 0.003 = req_acc_FO ! Required accuracy (-1=ignored, and use the
                           ! number of points and iter. below)
# These numbers are ignored except if req_acc_FO is equal to -1
 5000 = npoints_FO_grid ! number of points to setup grids
 4 = niters_FO_grid ! number of iter. to setup grids
 10000 = npoints_FO ! number of points to compute Xsec
 6 = niters_FO ! number of iter. to compute Xsec
#***********************************************************************
# Random number seed *
#***********************************************************************
     0 = iseed ! rnd seed (0=assigned automatically=default))
#***********************************************************************
# Collider type and energy *
#***********************************************************************
    1 = lpp1 ! beam 1 type (0 = no PDF)
    1 = lpp2 ! beam 2 type (0 = no PDF)
 6500 = ebeam1 ! beam 1 energy in GeV
 6500 = ebeam2 ! beam 2 energy in GeV
#***********************************************************************
# PDF choice: this automatically fixes also alpha_s(MZ) and its evol. *
#***********************************************************************
  lhapdf = pdlabel ! PDF set
  21100 = lhaid ! if pdlabel=lhapdf, this is the lhapdf number
#***********************************************************************
# Include the NLO Monte Carlo subtr. terms for the following parton *
# shower (HERWIG6 | HERWIGPP | PYTHIA6Q | PYTHIA6PT | PYTHIA8) *
# WARNING: PYTHIA6PT works only for processes without FSR!!!! *
#***********************************************************************
  HERWIG6 = parton_shower
#***********************************************************************
# Renormalization and factorization scales *
# (Default functional form for the non-fixed scales is the sum of *
# the transverse masses of all final state particles and partons. This *
# can be changed in SubProcesses/set_scales.f) *
#***********************************************************************
 F = fixed_ren_scale ! if .true. use fixed ren scale
 F = fixed_fac_scale ! if .true. use fixed fac scale
 91.188 = muR_ref_fixed ! fixed ren reference scale
 91.188 = muF1_ref_fixed ! fixed fact reference scale for pdf1
 91.188 = muF2_ref_fixed ! fixed fact reference scale for pdf2
#***********************************************************************
# Renormalization and factorization scales (advanced and NLO options) *
#***********************************************************************
 F = fixed_QES_scale ! if .true. use fixed Ellis-Sexton scale
 91.188 = QES_ref_fixed ! fixed Ellis-Sexton reference scale
 1 = muR_over_ref ! ratio of current muR over reference muR
 1 = muF1_over_ref ! ratio of current muF1 over reference muF1
 1 = muF2_over_ref ! ratio of current muF2 over reference muF2
 1 = QES_over_ref ! ratio of current QES over reference QES
#***********************************************************************
# Reweight flags to get scale dependence and PDF uncertainty *
# For scale dependence: factor rw_scale_up/down around central scale *
# For PDF uncertainty: use LHAPDF with supported set *
#***********************************************************************
 .true. = reweight_scale ! reweight to get scale dependence
  0.5 = rw_Rscale_down ! lower bound for ren scale variations
  2.0 = rw_Rscale_up ! upper bound for ren scale variations
  0.5 = rw_Fscale_down ! lower bound for fact scale variations
  2.0 = rw_Fscale_up ! upper bound for fact scale variations
 .true. = reweight_PDF ! reweight to get PDF uncertainty
  21101 = PDF_set_min ! First of the error PDF sets
  21140 = PDF_set_max ! Last of the error PDF sets
#***********************************************************************
# Merging - WARNING! Applies merging only at the hard-event level. *
# After showering an MLM-type merging should be applied as well. *
# See http://amcatnlo.cern.ch/FxFx_merging.htm for more details. *
#***********************************************************************
 0 = ickkw ! 0 no merging, 3 FxFx merging
#***********************************************************************
#
#***********************************************************************
# BW cutoff (M+/-bwcutoff*Gamma) *
#***********************************************************************
 15 = bwcutoff
#***********************************************************************
# Cuts on the jets *
# When matching to a parton shower, these generation cuts should be *
# considerably softer than the analysis cuts. *
# (more specific cuts can be specified in SubProcesses/cuts.f) *
#***********************************************************************
  -1 = jetalgo ! FastJet jet algorithm (1=kT, 0=C/A, -1=anti-kT)
 0.5 = jetradius ! The radius parameter for the jet algorithm
  30 = ptj ! Min jet transverse momentum
   4 = etaj ! Max jet abs(pseudo-rap) (a value .lt.0 means no cut)
#***********************************************************************
# Cuts on the charged leptons (e+, e-, mu+, mu-, tau+ and tau-) *
# (more specific gen cuts can be specified in SubProcesses/cuts.f) *
#***********************************************************************
   0 = ptl ! Min lepton transverse momentum
  -1 = etal ! Max lepton abs(pseudo-rap) (a value .lt.0 means no cut)
   0 = drll ! Min distance between opposite sign lepton pairs
  30 = mll ! Min inv. mass of all oppositely charged lepton pairs
#***********************************************************************
# Photon-isolation cuts, according to hep-ph/9801442 *
# When ptgmin=0, all the other parameters are ignored *
#***********************************************************************
  20 = ptgmin ! Min photon transverse momentum
   2 = etagamma ! Max photon abs(pseudo-rap)
 0.7 = R0gamma ! Radius of isolation code
 1.0 = xn ! n parameter of eq.(3.4) in hep-ph/9801442
 1.0 = epsgamma ! epsilon_gamma parameter of eq.(3.4) in hep-ph/9801442
 .true. = isoEM ! isolate photons from EM energy (photons and leptons)
#***********************************************************************
# maximal pdg code for quark to be considered as a jet *
#***********************************************************************
 5 = maxjetflavor
#***********************************************************************
######################################################################
## 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. By default, ##
## this is only 1->2 decay modes. ##
## ##
######################################################################

###################################
## INFORMATION FOR LOOP
###################################
Block loop
    1 9.118800e+01 # MU_R

###################################
## INFORMATION FOR MASS
###################################
Block mass
    6 1.732000e+02 # MT
   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 0.000000 # d : 0.0
  2 0.000000 # u : 0.0
  3 0.000000 # s : 0.0
  4 0.000000 # c : 0.0
  5 0.000000 # b : 0.0
  11 0.000000 # e- : 0.0
  12 0.000000 # ve : 0.0
  13 0.000000 # mu- : 0.0
  14 0.000000 # vm : 0.0
  16 0.000000 # vt : 0.0
  21 0.000000 # g : 0.0
  22 0.000000 # a : 0.0
  24 80.419002 # w+ : cmath.sqrt(MZ__exp__2/2. + cmath.sqrt(MZ__exp__4/4. - (aEW*cmath.pi*MZ__exp__2)/(Gf*sqrt__2)))
  82 0.000000 # gh : 0.0

###################################
## INFORMATION FOR SMINPUTS
###################################
Block sminputs
    1 1.325070e+02 # aEWM1
    2 1.166390e-05 # Gf
    3 1.180000e-01 # aS

###################################
## INFORMATION FOR YUKAWA
###################################
Block yukawa
    6 1.732000e+02 # ymt
   15 1.777000e+00 # ymtau

###################################
## INFORMATION FOR DECAY
###################################
DECAY 6 0.000000e+00 # WT
DECAY 23 0.000000e+00 # WZ
DECAY 24 0.000000e+00 # WW
DECAY 25 0.000000e+00 # 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 0.000000 # d : 0.0
DECAY 2 0.000000 # u : 0.0
DECAY 3 0.000000 # s : 0.0
DECAY 4 0.000000 # c : 0.0
DECAY 5 0.000000 # b : 0.0
DECAY 11 0.000000 # e- : 0.0
DECAY 12 0.000000 # ve : 0.0
DECAY 13 0.000000 # mu- : 0.0
DECAY 14 0.000000 # vm : 0.0
DECAY 15 0.000000 # ta- : 0.0
DECAY 16 0.000000 # vt : 0.0
DECAY 21 0.000000 # g : 0.0
DECAY 22 0.000000 # a : 0.0
DECAY 82 0.000000 # gh : 0.0
#===========================================================
# QUANTUM NUMBERS OF NEW STATE(S) (NON SM PDG CODE)
#===========================================================

Block QNUMBERS 82 # gh
        1 0 # 3 times electric charge
        2 1 # number of spin states (2S+1)
        3 8 # colour rep (1: singlet, 3: triplet, 8: octet)
        4 1 # Particle/Antiparticle distinction (0=own anti)

Question information

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Status:
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MadGraph5_aMC@NLO Edit question
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Solved by:
Pia Bredt
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Last reply:
Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

So I have run with the default run_card the following code

> import model loop_sm-no_b_mass
> set complex_mass_scheme
> generate p p > z j QCD=1 QED=1 [QCD]
> output
> launch
> fixed_order=ON

Here are the result for various version of the code

3.3.1: 2.923e+04 +- 1.7e+02 pb [scale variation +4% -8%]
3.1.0: 2.920e+04 +- 1.5e+02 pb [official first version of 3.x branch]
3.0.2.beta: (based on 2.6.4) 2.938e+04 +- 1.5e+02 pb
3.0.0.beta: (based on 2.6.2) 2.982e+04 +- 1.7e+02 pb

2.9.7: 2.925e+04 +- 1.9e+02 pb [scale variation +4% -8%]
2.9.3: 2.925e+04 +- 1.9e+02 pb
2.9.2: 2.919e+04 +- 1.9e+02 pb
2.7.1: 2.934e+04 pb
2.6.5: 2.936e+04 +- 1.9e+02 pb
2.6.3: 2.936e+04 +- 1.9e+02 pb
2.6.2: 2.936e+04 +- 1.9e+02 pb
2.6.1: 2.936e+04 +- 1.9e+02 pb [base for 3.0.0 branch]
2.6.0: 2.936e+04 +- 1.9e+02 pb
2.5.5: 2.938e+04 +- 1.9e+02 pb

Since 3.0.0, is based on 2.6.2 and was a first beta version, it is strongly not recomended to not use that version of the code.

So I guess that this is related to the bug reported in the UpdateNote of the release of the beta version of 3.0.1:
     RF: Fixed a major bug in the code that affected 3.0.0 that affected processes with
         cuts and --to a lesser extend-- processes with massive final state particles:
         the phase-space region where "xi_i_fks != xinorm*xi_i_hat" had the wrong "prefact".

Cheers,

Olivier

PS: The only two version currently supported are 2.9.7 (long term stable where 2.9.8 will only contain bug fix but no new features) and 3.3.1 which is a more standard release.
Both 2.6.5 and 3.0.0 are more than 3 year old and out of support.

> On 6 Dec 2021, at 18:20, Pia Bredt <email address hidden> wrote:
>
> MG5_aMC>import model loop_sm-no_b_mass
> MG5_aMC>set complex_mass_scheme
> MG5_aMC>generate p p > z j QCD=1 QED=1 [QCD]

Revision history for this message
Pia Bredt (bredtpia) said : 		#2

Hi Olivier,

Thanks a lot for the very detailed answer!
Helped very much.

Cheers,
Pia