Negative cross-section when generating p p > j j at NLO
I am trying to generate p p > j j at fixed order NLO on the parton level. Whenever I do this I produce a negative cross-section;
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Final results and run summary:
Process p p > j j [QCD]
Run at p-p collider (7000.0 + 7000.0 GeV)
Total cross section: -5.229e+08 +- 3.9e+06 pb
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Scale variation (computed from histogram information):
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My Banner text is as follows:
<LesHouchesEvents version="3.0">
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# 1. software version *
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3.5.0.alpha
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# Number of LHE events (and their normalization) and the required *
# (relative) accuracy on the Xsec. *
# These values are ignored for fixed order runs *
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10000 = nevents ! Number of unweighted events requested
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! (-1= no split).
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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
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0 = iseed ! rnd seed (0=assigned automatically=
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# Collider type and energy *
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# 1/-1 = proton/antiproton *
# 3/-3 = electron/positron with ISR/Beamstrahlung; *
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1 = lpp1 ! beam 1 type (0 = no PDF)
1 = lpp2 ! beam 2 type (0 = no PDF)
7000.0 = ebeam1 ! beam 1 energy in GeV
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nn23nlo = pdlabel ! PDF set
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0 = pdfscheme ! the scheme of the input PDFs. 0->MSbar; 1->DIS
! 2->eta (leptonic); 3->beta (leptonic)
! 4->mixed (leptonic); 6->delta (leptonic)
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# The following block is specific to lepton collisions (lpp=+-3) *
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True = photons_from_lepton ! whether to include or not photons from
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# shower (HERWIG6 | HERWIGPP | PYTHIA6Q | PYTHIA6PT | PYTHIA8) *
# WARNING: PYTHIA6PT works only for processes without FSR!!!! *
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HERWIG6 = parton_shower
1.0 = shower_scale_factor ! multiply default shower starting
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# 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
-1 = 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
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# Reweight variables for scale dependence and PDF uncertainty *
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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.
False = reweight_pdf ! Reweight to get PDF uncertainty. Should be a
! list booleans of equal length to lhaid to specify for
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# -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph]. *
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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
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# Fermion-photon recombination parameters *
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0.1 = rphreco ! Minimum fermion-photon distance for recombination
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False = quarkphreco ! Recombine photons and quarks together
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# When ptgmin=0, all the other parameters are ignored *
# More specific cuts can be specified in SubProcesses/cuts.f *
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20.0 = 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
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<slha>
#######
## PARAM_CARD AUTOMATICALY GENERATED BY MG5 ####
#######
#######
## INFORMATION FOR MASS
#######
BLOCK MASS #
5 4.700000e+00 # mb
6 1.730000e+02 # mt
15 1.777000e+00 # mta
23 9.118800e+01 # mz
25 1.250000e+02 # mh
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
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 8.041900e+01 # w+ : cmath.sqrt(
#######
## INFORMATION FOR SMINPUTS
#######
BLOCK SMINPUTS #
1 1.325070e+02 # aewm1
2 1.166390e-05 # gf
3 1.190000e-01 # as (note that parameter not used if you use a pdf set)
#######
## INFORMATION FOR YUKAWA
#######
BLOCK YUKAWA #
5 4.700000e+00 # ymb
6 1.730000e+02 # ymt
15 1.777000e+00 # ymtau
#######
## INFORMATION FOR DECAY
#######
DECAY 6 1.491500e+00 # wt
DECAY 23 2.441404e+00 # wz
DECAY 24 2.047600e+00 # ww
DECAY 25 6.382339e-03 # wh
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
#######
## INFORMATION FOR QNUMBERS 82
#######
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/
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#
# This file contains the settings for analyses to be linked to fixed
# order runs. Analysis files are meant to be put (or linked) inside
# <PROCDIR>
# process directory). See the
# <PROCDIR>
# on how to write your own analysis.
#
#######
#
# Analysis format.
# Can either be 'topdrawer', 'root', 'HwU', 'LHE' or 'none'.
# When choosing HwU, it comes with a GnuPlot wrapper. When choosing
# topdrawer, the histogramming package 'dbook.f' is included in the
# code, while when choosing root the 'rbook_fe8.f' and 'rbook_be8.cc'
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# to be set empty.
FO_ANALYSIS_FORMAT = HwU
#
#
# Needed extra-libraries (FastJet is already linked):
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# (Absolute) path to the extra libraries. Directory names should be
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# (Absolute) path to the dirs containing header files needed by the
# libraries (e.g. C++ header files):
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# User's analysis (to be put in the <PROCDIR>
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#
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## example on lxplus (CERN) as of July 2014. When using this, comment
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## e.g. /afs/cern.
#FO_ANALYSIS_FORMAT = root
#FO_EXTRALIBS = Core Cint Hist Matrix MathCore RIO dl Thread
#FO_EXTRAPATHS = <PATH_TO_ROOT>/lib
#FO_INCLUDEPATHS = <PATH_TO_
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# ADDED MYSELF:
FO_LHE_
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<run_settings>
order = NLO
fixed_order = ON
shower = OFF
madspin = OFF
reweight = OFF
madanalysis = OFF
runshower = False
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</header>
</LesHouchesEvents>
Does anyone know why this error occurs?
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