K-factor of ttb process
Dear MadGraph Team,
We have been trying to compute the cross-section of ttb process with the NLO-type generation. In order to do so we use the 5f scheme by importing the model 'sm-no_b_mass'. We copy below the run_cardNLOtype.dat file that we have used for running MadGraph5_aMC@NLO (version 2.6.0). We have obtained the following results:
-------
NLO-type generation-ttb
-------
xs_LO = 2.7 +- 0.01 pb
Scale uncertainty = +33% -24%
PDF uncertainty = +4% -5%
xs_NLO = 34.04 +- 1.8 pb
Scale uncertainty = +53% -32%
PDF uncertainty = +3% -4%
which give us a huge K-factor of 12.6. However, if we do the same computation for ttj, we obtain:
-------
NLO-type generation-ttj
-------
xs_LO = 315.5 +- 1.4 pb
Scale uncertainty = +45% -29%
PDF uncertainty = +2% -3%
xs_NLO = 415.4 +- 7.3 pb
Scale uncertainty = +9% -13%
PDF uncertainty = +2% -3%
so that we have a K-factor=1.32. This result is consistent with what you show in the table 5 of your paper arXiv:1405.0301 [hep-ph].
Taking into account the above results and the fact that the multiparticle 'j' already includes the b-quark, then we would like to understand if the K-factor obtained by including explicitly the b-quark in the final state is reliable. In other words, is it correct to generate the ttb@NLO in this way?
Thank you very much for your help.
Ernesto Arganda.
The run_cardNLOtype.dat file is:
#******
# MadGraph5_aMC@NLO *
# *
# run_card.dat aMC@NLO *
# *
# This file is used to set the parameters of the run. *
# *
# Some notation/
# *
# 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 *
#******
1000 = nevents ! Number of unweighted events requested
-1.0 = req_acc ! Required accuracy (-1=auto determined from nevents)
-1 = 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) *
#******
0.1 = req_acc_FO ! Required accuracy (-1=ignored, and use the
# 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=
#******
# Collider type and energy *
#******
1 = lpp1 ! beam 1 type (0 = no PDF)
1 = lpp2 ! beam 2 type (0 = no PDF)
6500.0 = ebeam1 ! beam 1 energy in GeV
6500.0 = 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. 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!!!! *
#******
HERWIG6 = parton_shower
1.0 = shower_scale_factor ! multiply default shower starting
#******
# 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/
# dynamical_
#******
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
3 = dynamical_
! 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_
! 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://
# 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]. *
#******
0 = ickkw
#******
#
#******
# BW cutoff (M+/-bwcutoff*
# 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)
0.5 = jetradius ! The radius parameter for the jet algorithm
30.0 = ptj ! Min jet transverse momentum
4.0 = 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 *
#******
20.0 = ptgmin ! Min photon transverse momentum
2.0 = 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)
#******
# For aMCfast+APPLGRID use in PDF fitting (http://
#******
0 = iappl ! aMCfast switch (0=OFF, 1=prepare grids, 2=fill grids)
#******
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