NLO tt~ cross-section

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.

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

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.

Thanks Olivier Mattelaer, that solved my question.