cross section change in tttj production between different MadGraph versions

Hi,

I'm generating 3top events separately for tttj and tttW. I have observed a change in the cross section for tttj when I move from MGv2.9.9 to MGv3.3.2. This doesn't happen to tttW. For both versions, I'm using the same parameter card and run card. The only exception is dsqrt_shat in the run card, which only becomes available for more recent version of MG. This option isn't usable for MGv2.9.9 but is set to 0.0 for MGv3.3.2.

The cross sections I obtained are as following:
2.9.9: 0.0004096 +- 7.459e-07 pb
3.3.2: 0.0003871 +- 7.028e-07 pb
I tested more versions than these two (2.9.5, 3.3.1, 3.5.3) and can confirm that this is a stable change after 2.9.9.
Could you please help understanding the source of the difference?

I attached the cards below.

Thanks a lot in advance for your help!

Regards, Quake

process card:
set group_subprocesses Auto
set ignore_six_quark_processes False
set max_t_for_channel 99
set loop_optimized_output True
set low_mem_multicore_nlo_generation False
set default_unset_couplings 99
set zerowidth_tchannel True
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model sm-no_b_mass
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
define j = p
define p = g u c d s u~ c~ d~ s~
define p = p b b~
define j = g u c d s u~ c~ d~ s~
define j = j b b~
generate p p > t t~ t j QED=4
add process p p > t t~ t~ j QED=4

param_card:
###################################
## INFORMATION FOR MASS
###################################
Block mass
    6 1.725000e+02 # MT
   15 1.776820e+00 # MTA
   23 9.118760e+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
  4 0.000000e+00 # c : 0.0
  5 0.000000e+00 # b : 0.0
  11 0.000000e+00 # e- : 0.0
  12 0.000000e+00 # ve : 0.0
  13 0.000000e+00 # mu- : 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 8.039900e+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 1.323489e+02 # aEWM1
    2 1.166370e-05 # Gf
    3 1.184000e-01 # aS (Note that Parameter not used if you use a PDF set)

###################################
## INFORMATION FOR YUKAWA
###################################
Block yukawa
    6 1.725000e+02 # ymt
   15 1.777000e+00 # ymtau

###################################
## INFORMATION FOR DECAY
###################################
DECAY 6 1.320000e+00 # WT
DECAY 23 2.495200e+00 # WZ
DECAY 24 2.085000e+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 15 0.000000e+00 # ta- : 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 for MGv2.9.9:
#*********************************************************************
# 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 *
#*********************************************************************
  20000 = 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, 4=photon from muon *
#*********************************************************************
  1 = lpp1 ! beam 1 type
  1 = lpp2 ! beam 2 type
  6500.0 = ebeam1 ! beam 1 total energy in GeV
  6500.0 = ebeam2 ! beam 2 total energy in GeV
# To see polarised beam options: type "update beam_pol"

#*********************************************************************
# PDF CHOICE: this automatically fixes also alpha_s and its evol. *
#*********************************************************************
  lhapdf = pdlabel ! PDF set
  260000 = 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"

#*********************************************************************
#
#*********************************************************************
# Phase-Space Optimization strategy (basic options)
#*********************************************************************
  0 = nhel ! using helicities importance sampling or not.
! 0: sum over helicity, 1: importance sampling
  1 = sde_strategy ! default integration strategy (hep-ph/2021.00773)
! 1 is old strategy (using amp square)
! 2 is new strategy (using only the denominator)
# To see advanced option for Phase-Space optimization: type "update psoptim"
#*********************************************************************
# 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) *
#*********************************************************************
  20.0 = ptj ! minimum pt for the jets
  -1.0 = ptjmax ! maximum pt for the jets
  {} = 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})
#
# For display option for energy cut in the partonic center of mass frame type 'update ecut'
#
#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  5.0 = etaj ! max rap for the jets
  {} = 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 *
#*********************************************************************
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
#*********************************************************************
  {} = 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.
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
  0.0 = ptheavy ! minimum pt for at least one heavy final state
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
  5 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: Do not use for interference type of computation *
#*********************************************************************
  True = use_syst ! Enable systematics studies
#
  systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
  ['--mur=0.5,1.0,2.0', '--dyn=-1', '--muf=0.5,1.0,2.0', '--weight_info=MUR%(mur).1f_MUF%(muf).1f_PDF%(pdf)i', '--pdf=NNPDF30_nlo_as_0118,PDF4LHC15_nlo_30_pdfas,NNPDF30_nlo_as_0119@0,NNPDF30_nlo_as_0117@0,CT14nlo@0,MMHT2014nlo68clas118@0', '--remove_wgts=".*MUR0.5_MUF2.0.*|.*MUR2.0_MUF0.5.*"'] = 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'
  3.0 = lhe_version
  12345 = python_seed

run_card for MGv3.3.2:
#*********************************************************************
# 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 *
#*********************************************************************
  20000 = 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=elastic photon of proton,*
# +/-3=PDF of electron/positron beam *
# +/-4=PDF of muon/antimuon beam *
#*********************************************************************
  1 = lpp1 ! beam 1 type
  1 = lpp2 ! beam 2 type
  6500.0 = ebeam1 ! beam 1 total energy in GeV
  6500.0 = ebeam2 ! beam 2 total energy in GeV
# To see polarised beam options: type "update beam_pol"

#*********************************************************************
# PDF CHOICE: this automatically fixes alpha_s and its evol. *
# pdlabel: lhapdf=LHAPDF (installation needed) [1412.7420] *
# iww=Improved Weizsaecker-Williams Approx.[hep-ph/9310350] *
# eva=Effective W/Z/A Approx. [21yy.zzzzz] *
# none=No PDF, same as lhapdf with lppx=0 *
#*********************************************************************
  lhapdf = pdlabel ! PDF set
  260000 = 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"

#*********************************************************************
#
#*********************************************************************
# Phase-Space Optimization strategy (basic options)
#*********************************************************************
  0 = nhel ! using helicities importance sampling or not.
! 0: sum over helicity, 1: importance sampling
  1 = sde_strategy ! default integration strategy (hep-ph/2021.xxxxx)
! 1 is old strategy (using amp square)
! 2 is new strategy (using only the denominator)
# To see advanced option for Phase-Space optimization: type "update psoptim"
#*********************************************************************
# 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 *
#*******************************
  0.0 = dsqrt_shat ! minimal shat for full process
#
#
#*********************************************************************
# 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) *
#*********************************************************************
  20.0 = ptj ! minimum pt for the jets
  -1.0 = ptjmax ! maximum pt for the jets
  {} = 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})
#
# For display option for energy cut in the partonic center of mass frame type 'update ecut'
#
#*********************************************************************
# Maximum and minimum absolute rapidity (for max, -1 means no cut) *
#*********************************************************************
  5.0 = etaj ! max rap for the jets
  {} = 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 *
#*********************************************************************
#*********************************************************************
# Minimum and maximum invariant mass for pairs *
#*********************************************************************
  {} = 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.
#*********************************************************************
# Inclusive cuts *
#*********************************************************************
  0.0 = ptheavy ! minimum pt for at least one heavy final state
#*********************************************************************
# maximal pdg code for quark to be considered as a light jet *
# (otherwise b cuts are applied) *
#*********************************************************************
  5 = maxjetflavor ! Maximum jet pdg code
#*********************************************************************
#
#*********************************************************************
# Store info for systematics studies *
# WARNING: Do not use for interference type of computation *
#*********************************************************************
  True = use_syst ! Enable systematics studies
#
  systematics = systematics_program ! none, systematics [python], SysCalc [depreceted, C++]
  ['--weight_info=MUR%(mur).1f_MUF%(muf).1f_PDF%(pdf)i', '--remove_wgts=".*MUR0.5_MUF2.0.*|.*MUR2.0_MUF0.5.*"', '--pdf=NNPDF30_nlo_as_0118,PDF4LHC21_40_pdfas,NNPDF30_nlo_as_0119@0,NNPDF30_nlo_as_0117@0,NNPDF30_nnlo_as_0118_hessian@0,MSHT20nnlo_as118@0,MSHT20nlo_as118@0,CT18NNLO@0,CT18NLO@0,NNPDF31_nnlo_as_0118_hessian@0,NNPDF31_nlo_as_0118_hessian@0,NNPDF40_nnlo_as_01180_hessian@0,NNPDF40_nnlo_as_01180@0,CT18ANNLO@0,CT18XNNLO@0,CT18ZNNLO@0', '--muf=0.5,1.0,2.0', '--mur=0.5,1.0,2.0', '--dyn=-1'] = systematics_arguments ! see: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Systematics#Systematicspythonmodule
  3.0 = lhe_version
  12345 = python_seed