NLO tt~ cross-section

Asked by Amin Aboubrahim on 2018-03-12

Dear experts,

I am generating t tbar production at NLO:

import model loop_sm-no_b_mass -name
define X = t t~
generate p p > X X QED=0 [QCD] @0
add process p p > X X j QED=0 [QCD] @1
add process p p > X X j j QED=0 [QCD] @2

I am setting the proper cuts on ptj and others in the run_card and the QCUT in the shower_card. Despite this I am getting a cross-section more than twice the one obtained at LO (parton level cross-section). I do not know what the cross-section is after showering since I am getting a crash with PYTHIA8. But first I need to understand what I am doing wrong at the hard process level (maybe something wrong with generator level cuts). I should mention also that the grid set up takes a long time (5+ hours).
I will paste the run_card and shower_card here. I have not changed anything in the param_card.

#***********************************************************************
# 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 *
# *
# Some of the values of variables can be list. These can either be *
# comma or space separated. *
#***********************************************************************
#
#*******************
# Running parameters
#*******************
#
#***********************************************************************
# Tag name for the run (one word) *
#***********************************************************************
  tag_1 = run_tag ! name of the run
#***********************************************************************
# Number of LHE 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
 -1.0 = req_acc ! Required accuracy (-1=auto determined from nevents)
 500 = nevt_job! Max number of events per job in event generation.
                 ! (-1= no split).
#***********************************************************************
# Normalize the weights of LHE events such that they sum or average to *
# the total cross section *
#***********************************************************************
 average = event_norm ! valid settings: average, sum, bias
#***********************************************************************
# Number of points per itegration channel (ignored for aMC@NLO runs) *
#***********************************************************************
 0.01 = 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)
 7000.0 = ebeam1 ! beam 1 energy in GeV
 7000.0 = ebeam2 ! beam 2 energy in GeV
#***********************************************************************
# PDF choice: this automatically fixes also alpha_s(MZ) and its evol. *
#***********************************************************************
 lhapdf = pdlabel ! PDF set
 231000 = lhaid ! If pdlabel=lhapdf, this is the lhapdf number. Only
              ! numbers for central PDF sets are allowed. Can be a list;
              ! PDF sets beyond the first are included via reweighting.
#***********************************************************************
# 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!!!! *
#***********************************************************************
  PYTHIA8 = parton_shower
  1.0 = shower_scale_factor ! multiply default shower starting
                                  ! scale by this factor
#***********************************************************************
# Renormalization and factorization scales *
# (Default functional form for the non-fixed scales is the sum of *
# the transverse masses divided by two of all final state particles *
# and partons. This can be changed in SubProcesses/set_scales.f or via *
# dynamical_scale_choice option) *
#***********************************************************************
 False = fixed_ren_scale ! if .true. use fixed ren scale
 False = fixed_fac_scale ! if .true. use fixed fac scale
 91.118 = muR_ref_fixed ! fixed ren reference scale
 91.118 = muF_ref_fixed ! fixed fact reference scale
 -1 = dynamical_scale_choice ! Choose one (or more) of the predefined
           ! dynamical choices. Can be a list; scale choices beyond the
           ! first are included via reweighting
 1.0 = muR_over_ref ! ratio of current muR over reference muR
 1.0 = muF_over_ref ! ratio of current muF over reference muF
#***********************************************************************
# Reweight variables for scale dependence and PDF uncertainty *
#***********************************************************************
 1.0, 2.0, 0.5 = rw_rscale ! muR factors to be included by reweighting
 1.0, 2.0, 0.5 = rw_fscale ! muF factors to be included by reweighting
 True = reweight_scale ! Reweight to get scale variation using the
            ! rw_rscale and rw_fscale factors. Should be a list of
            ! booleans of equal length to dynamical_scale_choice to
            ! specify for which choice to include scale dependence.
 True = reweight_PDF ! Reweight to get PDF uncertainty. Should be a
            ! list booleans of equal length to lhaid to specify for
            ! which PDF set to include the uncertainties.
#***********************************************************************
# Store reweight information in the LHE file for off-line model- *
# parameter reweighting at NLO+PS accuracy *
#***********************************************************************
 False = store_rwgt_info ! Store info for reweighting in LHE file
#***********************************************************************
# ickkw parameter: *
# 0: No merging *
# 3: FxFx 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 details. *
# 4: UNLOPS merging (with pythia8 only). No interface from within *
# MG5_aMC available, but available in Pythia8. *
# -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph]. *
#***********************************************************************
 3 = ickkw
#***********************************************************************
#
#***********************************************************************
# BW cutoff (M+/-bwcutoff*Gamma). Determines which resonances are *
# written in the LHE event file *
#***********************************************************************
 15.0 = bwcutoff
#***********************************************************************
# Cuts on the jets. Jet clustering is performed by FastJet. *
# - 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 *
#***********************************************************************
  1.0 = jetalgo ! FastJet jet algorithm (1=kT, 0=C/A, -1=anti-kT)
  0.7 = jetradius ! The radius parameter for the jet algorithm
 20.0 = ptj ! Min jet transverse momentum
 -1.0 = 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 cuts can be specified in SubProcesses/cuts.f *
#***********************************************************************
  0.0 = ptl ! Min lepton transverse momentum
 -1.0 = etal ! Max lepton abs(pseudo-rap) (a value .lt.0 means no cut)
  0.0 = drll ! Min distance between opposite sign lepton pairs
  0.0 = drll_sf ! Min distance between opp. sign same-flavor lepton pairs
  0.0 = mll ! Min inv. mass of all opposite sign lepton pairs
 30.0 = mll_sf ! Min inv. mass of all opp. sign same-flavor lepton pairs
#***********************************************************************
# Photon-isolation cuts, according to hep-ph/9801442. When ptgmin=0, *
# all the other parameters are ignored. *
# More specific cuts can be specified in SubProcesses/cuts.f *
#***********************************************************************
 15.0 = ptgmin ! Min photon transverse momentum
 -1.0 = etagamma ! Max photon abs(pseudo-rap)
  0.4 = 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)
#***********************************************************************
# For aMCfast+APPLGRID use in PDF fitting (http://amcfast.hepforge.org)*
#***********************************************************************
 0 = iappl ! aMCfast switch (0=OFF, 1=prepare grids, 2=fill grids)
#***********************************************************************

#***********************************************************************
# MadGraph5_aMC@NLO *
# *
# shower_card.dat aMC@NLO *
# *
# This file is used to set the parameters for the shower. *
# *
# Some notation/conventions: *
# *
# Lines starting with a hash (#) are info or comments *
# *
# mind the format: variable = value # comment *
#***********************************************************************
#
#***********************************************************************
# Shower settings *
#***********************************************************************
# Number of events, jobs, errors, and random seeds *
#***********************************************************************
nevents = -1 # N evts to shower (< 0 = all)
nsplit_jobs = 50 # N jobs to run in parallel (< 100!!)
combine_td = T # combine the topdrawer/HwU files if nsplit_jobs>1
maxprint = 2 # N evts to print in the log
maxerrs = 0.1 # max fraction of errors
rnd_seed = 0 # 1st random seed (0 = default)
rnd_seed2 = 0 # 2nd random seed (0 = default) !ONLY FOR HWERIG6!
#***********************************************************************
# PDFs and non-perturbative modelling *
#***********************************************************************
pdfcode = 1 # 0 = internal, 1 = same as NLO, other = lhaglue
ue_enabled = F # underlying event
hadronize = T # hadronisation on/off !IGNORED BY HERWIG6!
lambda_5 = -1 # Lambda_5 (< 0 = default) !IGNORED BY PYTHIA8!
#***********************************************************************
# Stable or unstable particles *
#***********************************************************************
b_stable = F # set B hadrons stable
pi_stable = T # set pi0's stable
wp_stable = F # set w+'s stable
wm_stable = F # set w-'s stable
z_stable = F # set z0's stable
h_stable = F # set Higgs' stable
tap_stable = F # set tau+'s stable
tam_stable = F # set tau-'s stable
mup_stable = F # set mu+'s stable
mum_stable = F # set mu-'s stable
#***********************************************************************
# Mass of the b quark *
#***********************************************************************
b_mass = -1 # if < 0 = read from SubProcesses/MCmasses_*.inc
#***********************************************************************
# Special settings *
#***********************************************************************
is_4lep = F # T if 4-lepton production !ONLY FOR PYTHIA6!
is_bbar = F # T if bb~ production !ONLY FOR HERWIG6!
#***********************************************************************
# FxFx merging parameters !ONLY FOR PYTHIA8!
#***********************************************************************
Qcut = 80.0 # Merging scale
njmax = 2 # Maximal multiplicity in the merging#***********************************************************************
# Decay channels *
#***********************************************************************
# Syntax for HERWIG6 *
# DM_I = M > D1 D2 @ BR @ ME *
# corresponding to call to HWMODK(M,BR,ME,D1,D2) *
# I < 100, M is the decaying resonance, D1, D2, ... are the decay *
# products (up to five), BR is the branching ratio and ME is the type *
# of matrix element to be used in the decay. *
# BR's are correctly understood only if they add up to 1, and only if *
# no more than three modes are required for a given resonance. *
# WARNING: the order of decay products in > 2-body decays IS RELEVANT. *
# *
# Syntax for PYTHIA6 *
# DM_I = M > D1 D2 @ BR @ ME *
# WARNING: turning hadronisation off disables top decays *
# WARNING: 1 -> n decays (with n > 2) are handled through a sequence *
# of 1 -> 2 decays. *
# WARNING: entries BR and ME are ignored *
# *
# Syntax for HERWIG++ *
# DM_I = M > D1 D2 @ BR @ ME *
# WARNING: entries BR and ME are ignored *
# *
# Syntax for PYTHIA8 *
# DM_I = M:onIfAny = D1 D2 *
# or similar, according to the offical PYTHIA8 decay syntax, see *
# the online PYTHIA8 manual *
# WARNING: 1 -> n decays (with n > 2) are handled through a sequence *
# of 1 -> 2 decays. *
# *
# Examples *
# Z -> e+ e- or mu+ mu- with BR = 0.5 each, HERWIG6 *
# DM_1 = 23 > -11 11 @ 0.5d0 @ 100
# DM_2 = 23 > -13 13 @ 0.5d0 @ 100
# H -> ta+ ta- with BR = 1, HERWIG6 or HERWIG++ *
# DM_3 = 25 > -15 15 @ 1.0d0 @ 0
# t -> ve e+ b with BR = 1, HERWIG6 or HERWIG++ *
# DM_4 = 6 > 12 -11 5 @ 1d0 @ 100
# t -> ve e+ b with BR = 1, PYTHIA6 *
# DM_5 = 6 > 24 5 @ 1d0 @ 100
# DM_6 = 24 > 12 -11 @ 1d0 @ 100
# W+ -> ve e+, W- -> vm~ mu-, PYTHIA8 *
# DM_1 = 24:onMode = off
# DM_2 = 24:onPosIfAny = 11 12
# DM_3 = 24:onNegIfAny = 13 14
# W+ -> ve e+, W- -> ve~ e- and vm~ mu-, PYTHIA8 *
# DM_1 = 24:onMode = off
# DM_2 = 24:onIfAny = 11 12
# DM_3 = 24:onNegIfAny = 13 14
#***********************************************************************
# Extra libraries/analyses *
#***********************************************************************
# The following lines need to be changed if the user does not want to *
# create a StdHEP/HepMC file, but to directly run an own analysis (to *
# be placed in HWAnalyzer or analogous MCatNLO subfolders). *
# Please use files in those folders as examples. *
# Remember that if your analysis uses hbook or is in the HwU format, *
# you must also add to hbook.o or HwU.o to the ANALYSE list as well. *
#***********************************************************************
extralibs = pythia8 boost_iostreams z d dl stdc++ # Extra-libraries (not LHAPDF)
                                 # Default: "stdhep Fmcfio"
                                 # PYTHIA > 8.200 may require library dl
extrapaths = ../lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8//lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/zlib/lib # Path to the extra-libraries
                                 # Default: "../lib"
INCLUDEPATHS = # Path to header files needed by c++
                                 # Dir names separated by white spaces
ANALYSE = # User's analysis and histogramming
                                 # routines (please use .o as extension
                                 # and use spaces to separate files)

Hope you can help! Thank you.

Best,
Amin

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2018-03-13
Last query:
2018-03-13
Last reply:
2018-03-12

Hi,

Since before the parton shower you have a lot of double counting between the various process I do not see why you have to worry about.

You should just expect an efficiency in Pythia around 50% to compensate such double counting.

Cheers,

Olivier

> On 12 Mar 2018, at 02:33, Amin Aboubrahim <email address hidden> wrote:
>
> New question #665496 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/665496
>
> Dear experts,
>
> I am generating t tbar production at NLO:
>
> import model loop_sm-no_b_mass -name
> define X = t t~
> generate p p > X X QED=0 [QCD] @0
> add process p p > X X j QED=0 [QCD] @1
> add process p p > X X j j QED=0 [QCD] @2
>
> I am setting the proper cuts on ptj and others in the run_card and the QCUT in the shower_card. Despite this I am getting a cross-section more than twice the one obtained at LO (parton level cross-section). I do not know what the cross-section is after showering since I am getting a crash with PYTHIA8. But first I need to understand what I am doing wrong at the hard process level (maybe something wrong with generator level cuts). I should mention also that the grid set up takes a long time (5+ hours).
> I will paste the run_card and shower_card here. I have not changed anything in the param_card.
>
>
> #***********************************************************************
> # 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 *
> # *
> # Some of the values of variables can be list. These can either be *
> # comma or space separated. *
> #***********************************************************************
> #
> #*******************
> # Running parameters
> #*******************
> #
> #***********************************************************************
> # Tag name for the run (one word) *
> #***********************************************************************
> tag_1 = run_tag ! name of the run
> #***********************************************************************
> # Number of LHE 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
> -1.0 = req_acc ! Required accuracy (-1=auto determined from nevents)
> 500 = nevt_job! Max number of events per job in event generation.
> ! (-1= no split).
> #***********************************************************************
> # Normalize the weights of LHE events such that they sum or average to *
> # the total cross section *
> #***********************************************************************
> average = event_norm ! valid settings: average, sum, bias
> #***********************************************************************
> # Number of points per itegration channel (ignored for aMC@NLO runs) *
> #***********************************************************************
> 0.01 = 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)
> 7000.0 = ebeam1 ! beam 1 energy in GeV
> 7000.0 = ebeam2 ! beam 2 energy in GeV
> #***********************************************************************
> # PDF choice: this automatically fixes also alpha_s(MZ) and its evol. *
> #***********************************************************************
> lhapdf = pdlabel ! PDF set
> 231000 = lhaid ! If pdlabel=lhapdf, this is the lhapdf number. Only
> ! numbers for central PDF sets are allowed. Can be a list;
> ! PDF sets beyond the first are included via reweighting.
> #***********************************************************************
> # 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!!!! *
> #***********************************************************************
> PYTHIA8 = parton_shower
> 1.0 = shower_scale_factor ! multiply default shower starting
> ! scale by this factor
> #***********************************************************************
> # Renormalization and factorization scales *
> # (Default functional form for the non-fixed scales is the sum of *
> # the transverse masses divided by two of all final state particles *
> # and partons. This can be changed in SubProcesses/set_scales.f or via *
> # dynamical_scale_choice option) *
> #***********************************************************************
> False = fixed_ren_scale ! if .true. use fixed ren scale
> False = fixed_fac_scale ! if .true. use fixed fac scale
> 91.118 = muR_ref_fixed ! fixed ren reference scale
> 91.118 = muF_ref_fixed ! fixed fact reference scale
> -1 = dynamical_scale_choice ! Choose one (or more) of the predefined
> ! dynamical choices. Can be a list; scale choices beyond the
> ! first are included via reweighting
> 1.0 = muR_over_ref ! ratio of current muR over reference muR
> 1.0 = muF_over_ref ! ratio of current muF over reference muF
> #***********************************************************************
> # Reweight variables for scale dependence and PDF uncertainty *
> #***********************************************************************
> 1.0, 2.0, 0.5 = rw_rscale ! muR factors to be included by reweighting
> 1.0, 2.0, 0.5 = rw_fscale ! muF factors to be included by reweighting
> True = reweight_scale ! Reweight to get scale variation using the
> ! rw_rscale and rw_fscale factors. Should be a list of
> ! booleans of equal length to dynamical_scale_choice to
> ! specify for which choice to include scale dependence.
> True = reweight_PDF ! Reweight to get PDF uncertainty. Should be a
> ! list booleans of equal length to lhaid to specify for
> ! which PDF set to include the uncertainties.
> #***********************************************************************
> # Store reweight information in the LHE file for off-line model- *
> # parameter reweighting at NLO+PS accuracy *
> #***********************************************************************
> False = store_rwgt_info ! Store info for reweighting in LHE file
> #***********************************************************************
> # ickkw parameter: *
> # 0: No merging *
> # 3: FxFx 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 details. *
> # 4: UNLOPS merging (with pythia8 only). No interface from within *
> # MG5_aMC available, but available in Pythia8. *
> # -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph]. *
> #***********************************************************************
> 3 = ickkw
> #***********************************************************************
> #
> #***********************************************************************
> # BW cutoff (M+/-bwcutoff*Gamma). Determines which resonances are *
> # written in the LHE event file *
> #***********************************************************************
> 15.0 = bwcutoff
> #***********************************************************************
> # Cuts on the jets. Jet clustering is performed by FastJet. *
> # - 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 *
> #***********************************************************************
> 1.0 = jetalgo ! FastJet jet algorithm (1=kT, 0=C/A, -1=anti-kT)
> 0.7 = jetradius ! The radius parameter for the jet algorithm
> 20.0 = ptj ! Min jet transverse momentum
> -1.0 = 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 cuts can be specified in SubProcesses/cuts.f *
> #***********************************************************************
> 0.0 = ptl ! Min lepton transverse momentum
> -1.0 = etal ! Max lepton abs(pseudo-rap) (a value .lt.0 means no cut)
> 0.0 = drll ! Min distance between opposite sign lepton pairs
> 0.0 = drll_sf ! Min distance between opp. sign same-flavor lepton pairs
> 0.0 = mll ! Min inv. mass of all opposite sign lepton pairs
> 30.0 = mll_sf ! Min inv. mass of all opp. sign same-flavor lepton pairs
> #***********************************************************************
> # Photon-isolation cuts, according to hep-ph/9801442. When ptgmin=0, *
> # all the other parameters are ignored. *
> # More specific cuts can be specified in SubProcesses/cuts.f *
> #***********************************************************************
> 15.0 = ptgmin ! Min photon transverse momentum
> -1.0 = etagamma ! Max photon abs(pseudo-rap)
> 0.4 = 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)
> #***********************************************************************
> # For aMCfast+APPLGRID use in PDF fitting (http://amcfast.hepforge.org)*
> #***********************************************************************
> 0 = iappl ! aMCfast switch (0=OFF, 1=prepare grids, 2=fill grids)
> #***********************************************************************
>
>
>
> #***********************************************************************
> # MadGraph5_aMC@NLO *
> # *
> # shower_card.dat aMC@NLO *
> # *
> # This file is used to set the parameters for the shower. *
> # *
> # Some notation/conventions: *
> # *
> # Lines starting with a hash (#) are info or comments *
> # *
> # mind the format: variable = value # comment *
> #***********************************************************************
> #
> #***********************************************************************
> # Shower settings *
> #***********************************************************************
> # Number of events, jobs, errors, and random seeds *
> #***********************************************************************
> nevents = -1 # N evts to shower (< 0 = all)
> nsplit_jobs = 50 # N jobs to run in parallel (< 100!!)
> combine_td = T # combine the topdrawer/HwU files if nsplit_jobs>1
> maxprint = 2 # N evts to print in the log
> maxerrs = 0.1 # max fraction of errors
> rnd_seed = 0 # 1st random seed (0 = default)
> rnd_seed2 = 0 # 2nd random seed (0 = default) !ONLY FOR HWERIG6!
> #***********************************************************************
> # PDFs and non-perturbative modelling *
> #***********************************************************************
> pdfcode = 1 # 0 = internal, 1 = same as NLO, other = lhaglue
> ue_enabled = F # underlying event
> hadronize = T # hadronisation on/off !IGNORED BY HERWIG6!
> lambda_5 = -1 # Lambda_5 (< 0 = default) !IGNORED BY PYTHIA8!
> #***********************************************************************
> # Stable or unstable particles *
> #***********************************************************************
> b_stable = F # set B hadrons stable
> pi_stable = T # set pi0's stable
> wp_stable = F # set w+'s stable
> wm_stable = F # set w-'s stable
> z_stable = F # set z0's stable
> h_stable = F # set Higgs' stable
> tap_stable = F # set tau+'s stable
> tam_stable = F # set tau-'s stable
> mup_stable = F # set mu+'s stable
> mum_stable = F # set mu-'s stable
> #***********************************************************************
> # Mass of the b quark *
> #***********************************************************************
> b_mass = -1 # if < 0 = read from SubProcesses/MCmasses_*.inc
> #***********************************************************************
> # Special settings *
> #***********************************************************************
> is_4lep = F # T if 4-lepton production !ONLY FOR PYTHIA6!
> is_bbar = F # T if bb~ production !ONLY FOR HERWIG6!
> #***********************************************************************
> # FxFx merging parameters !ONLY FOR PYTHIA8!
> #***********************************************************************
> Qcut = 80.0 # Merging scale
> njmax = 2 # Maximal multiplicity in the merging#***********************************************************************
> # Decay channels *
> #***********************************************************************
> # Syntax for HERWIG6 *
> # DM_I = M > D1 D2 @ BR @ ME *
> # corresponding to call to HWMODK(M,BR,ME,D1,D2) *
> # I < 100, M is the decaying resonance, D1, D2, ... are the decay *
> # products (up to five), BR is the branching ratio and ME is the type *
> # of matrix element to be used in the decay. *
> # BR's are correctly understood only if they add up to 1, and only if *
> # no more than three modes are required for a given resonance. *
> # WARNING: the order of decay products in > 2-body decays IS RELEVANT. *
> # *
> # Syntax for PYTHIA6 *
> # DM_I = M > D1 D2 @ BR @ ME *
> # WARNING: turning hadronisation off disables top decays *
> # WARNING: 1 -> n decays (with n > 2) are handled through a sequence *
> # of 1 -> 2 decays. *
> # WARNING: entries BR and ME are ignored *
> # *
> # Syntax for HERWIG++ *
> # DM_I = M > D1 D2 @ BR @ ME *
> # WARNING: entries BR and ME are ignored *
> # *
> # Syntax for PYTHIA8 *
> # DM_I = M:onIfAny = D1 D2 *
> # or similar, according to the offical PYTHIA8 decay syntax, see *
> # the online PYTHIA8 manual *
> # WARNING: 1 -> n decays (with n > 2) are handled through a sequence *
> # of 1 -> 2 decays. *
> # *
> # Examples *
> # Z -> e+ e- or mu+ mu- with BR = 0.5 each, HERWIG6 *
> # DM_1 = 23 > -11 11 @ 0.5d0 @ 100
> # DM_2 = 23 > -13 13 @ 0.5d0 @ 100
> # H -> ta+ ta- with BR = 1, HERWIG6 or HERWIG++ *
> # DM_3 = 25 > -15 15 @ 1.0d0 @ 0
> # t -> ve e+ b with BR = 1, HERWIG6 or HERWIG++ *
> # DM_4 = 6 > 12 -11 5 @ 1d0 @ 100
> # t -> ve e+ b with BR = 1, PYTHIA6 *
> # DM_5 = 6 > 24 5 @ 1d0 @ 100
> # DM_6 = 24 > 12 -11 @ 1d0 @ 100
> # W+ -> ve e+, W- -> vm~ mu-, PYTHIA8 *
> # DM_1 = 24:onMode = off
> # DM_2 = 24:onPosIfAny = 11 12
> # DM_3 = 24:onNegIfAny = 13 14
> # W+ -> ve e+, W- -> ve~ e- and vm~ mu-, PYTHIA8 *
> # DM_1 = 24:onMode = off
> # DM_2 = 24:onIfAny = 11 12
> # DM_3 = 24:onNegIfAny = 13 14
> #***********************************************************************
> # Extra libraries/analyses *
> #***********************************************************************
> # The following lines need to be changed if the user does not want to *
> # create a StdHEP/HepMC file, but to directly run an own analysis (to *
> # be placed in HWAnalyzer or analogous MCatNLO subfolders). *
> # Please use files in those folders as examples. *
> # Remember that if your analysis uses hbook or is in the HwU format, *
> # you must also add to hbook.o or HwU.o to the ANALYSE list as well. *
> #***********************************************************************
> extralibs = pythia8 boost_iostreams z d dl stdc++ # Extra-libraries (not LHAPDF)
> # Default: "stdhep Fmcfio"
> # PYTHIA > 8.200 may require library dl
> extrapaths = ../lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8//lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/lib /home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/zlib/lib # Path to the extra-libraries
> # Default: "../lib"
> INCLUDEPATHS = # Path to header files needed by c++
> # Dir names separated by white spaces
> ANALYSE = # User's analysis and histogramming
> # routines (please use .o as extension
> # and use spaces to separate files)
>
>
> Hope you can help! Thank you.
>
> Best,
> Amin
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Amin Aboubrahim (amin83) said : #2

Thank you Olivier.
I am trying to compare the hard cross-sections at LO and NLO at fixed order. What I understood from your answer is that one has to compare cross-sections after the shower in order to get the K value. So the hard process cross-sections must not be used. Did I understand right?

Thank you,
Amin

Hi,

> I am trying to compare the hard cross-sections at LO and NLO at fixed order. What I understood from your answer is that one has to compare cross-sections after the shower in order to get the K value.

This make sense in general and indeed this is the advise way to compute K factor.
But in your case your process definition has multiple jet multiplicity leading to
double counting between your different process definition.

In order to remove such double counting, you have to choose a scheme
(default is MLM at LO and FxFx at NLO) which apply some sudakov factor on each multiplicity
to remove such double counting. Those factor are applied for those two method within the parton-shower.

Cheers,

Olivier

> On 12 Mar 2018, at 05:52, Amin Aboubrahim <email address hidden> wrote:
>
> Question #665496 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/665496
>
> Status: Answered => Open
>
> Amin Aboubrahim is still having a problem:
> Thank you Olivier.
> I am trying to compare the hard cross-sections at LO and NLO at fixed order. What I understood from your answer is that one has to compare cross-sections after the shower in order to get the K value. So the hard process cross-sections must not be used. Did I understand right?
>
> Thank you,
> Amin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Amin Aboubrahim (amin83) said : #4

Thank you. I will go for NLO+PS to calculate the K factor. However, I am having a crash:

INFO: Compiling MCatNLO for PYTHIA8...
/usr/bin/ld: cannot find -ld
collect2: error: ld returned 1 exit status
make: *** [Pythia82] Error 1
ude -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/include -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8/include \
          -I/home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/MCatNLO/include Pythia82.cc -o Pythia8.exe \
          -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8/lib -lpythia8 \
          -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/hepmc/include -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/hepmc/lib -lHepMC -L../lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8//lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/zlib/lib -lpythia8 -lboost_iostreams -lz -ld -ldl -lstdc++ \

Pythia8 compilation did not succeed, exiting

Error detected in "launch "
write debug file /home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
aMCatNLOError : Compilation failed, check /home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/mcatnlo.log for details

I checked that "ld" is in /usr/bin. Do I have to do extra installation steps when working with aMC@NLO?

Best,
Amin

HI,

That's a bug inside pythia8 if I'm correct.
You need to edit the script pythia8-config to remove the wrong argurment -ld

Cheers,

Olivier

> On 12 Mar 2018, at 06:16, Amin Aboubrahim <email address hidden> wrote:
>
> Question #665496 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/665496
>
> Status: Answered => Open
>
> Amin Aboubrahim is still having a problem:
> Thank you. I will go for NLO+PS to calculate the K factor. However, I am
> having a crash:
>
> INFO: Compiling MCatNLO for PYTHIA8...
> /usr/bin/ld: cannot find -ld
> collect2: error: ld returned 1 exit status
> make: *** [Pythia82] Error 1
> ude -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/include -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8/include \
> -I/home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/MCatNLO/include Pythia82.cc -o Pythia8.exe \
> -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8/lib -lpythia8 \
> -I/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/hepmc/include -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/hepmc/lib -lHepMC -L../lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/pythia8//lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/boost/lib -L/home/abouibrahim.a/MG5_aMC_v2_6_0/HEPTools/zlib/lib -lpythia8 -lboost_iostreams -lz -ld -ldl -lstdc++ \
>
> Pythia8 compilation did not succeed, exiting
>
> Error detected in "launch "
> write debug file /home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/run_01_tag_1_debug.log
> If you need help with this issue please contact us on https://answers.launchpad.net/mg5amcnlo
> aMCatNLOError : Compilation failed, check /home/abouibrahim.a/MG5_aMC_v2_6_0/bin/tt_qcd/mcatnlo.log for details
>
>
> I checked that "ld" is in /usr/bin. Do I have to do extra installation steps when working with aMC@NLO?
>
> Best,
> Amin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Amin Aboubrahim (amin83) said : #6

Thanks Olivier Mattelaer, that solved my question.