Bias in reweighted cross sections for NLO production with systematics

Asked by Kenneth Long on 2017-11-06

Hi experts,

I'm generating a simple process (p p > w+) to test the reweighting to many PDFs with v2.6.0. My input cards are in [1].

I then call the systematics program as

pdfsets="292200,303600,292600@0,305800,315000@0,"
pdfsets+="13100,13163@0,13167,13000@0,13065@0,"
pdfsets+="13069,13200@0,25200@0,25300@0,25000,"
pdfsets+="42400,42780@0,90200,91200,90400,"
pdfsets+="91400,61100,61130,61200,61230,"
pdfsets+="13400,82000"
scalevars="--mur=1,2,0.5 --muf=1,2,0.5 --together=muf,mur --dyn=-1"

./bin/aMCatNLO "systematics $1 --pdf=$pdfsets $scalevars"

The output I get is

#***************************************************************************
#
# original cross-section: 106033.6152
# scale variation: +-46.3% -55.5%
#
#PDF ABMP15_3_nnlo: 45793.2 +0.473% -0.473%
#PDF PDF4LHC15_nnlo_100_pdfas: 55969.7 +1.3% -1.3%
#PDF MMHT2014lo68cl: 51926.5 +0.713% -1.04%
#PDF PDF4LHC15_nlo_30_pdfas: 53743.5 +1.28% -1.28%
#PDF NNPDF30_nlo_nf_5_pdfas: 53187.3 +1.02% -1.02%
#PDF HERAPDF20_NLO_EIG: 57731.6 +0.448% -0.49%
#PDF CT14nlo: 54370 +1.28% -1.49%
#PDF NNPDF31_nnlo_as_0118: 56704.3 +0.524% -0.524%
#PDF NNPDF31_nlo_hessian_pdfas: 55194.6 +0.929% -0.929%
#PDF HERAPDF20_NNLO_EIG: 58950.4 +0.637% -0.675%
#PDF PDF4LHC15_nlo_100_pdfas: 53745 +1.29% -1.29%
#PDF LUXqed_plus_PDF4LHC15_nnlo_100: 55713.6 +1.08% -1.08%
#PDF PDF4LHC15_nnlo_30_pdfas: 55968.6 +1.24% -1.24%
#***************************************************************************

I've tried with both LHAPDF v6.1 and 6.2 and see the same thing. I also tried with p p > e+ e- and see the same effect. The weights have the same striking trend from scale specific weights (which look fine) to PDF weights. Is it possible that there is a systematic factor of 2 being lost somewhere?

Thanks,

Kenneth

[1] https://github.com/kdlong/genproductions/tree/mg260/bin/MadGraph5_aMCatNLO/cards/examples/wplustest_5f_NLO

Question information

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Last query:
2017-11-06
Last reply:
2017-11-07

Hi,

I have put the following line in the run_card.dat:
 [“--pdf=292200,292600@0,13100,13163@0,13167,13000@0,13065@0", "--mur=1,2,0.5"," --muf=1,2,0.5", "--dyn=-1"] = systematics_arguments

and get the following numbers which are much more reasonable.

INFO: #***************************************************************************
#
# original cross-section: 83570.9312275
# scale variation: +12.3% -13.2%
#
#PDF NNPDF30_nlo_nf_5_pdfas: 87998.3 +2.07% -2.07%
#PDF CT14nlo: 89749.3 +2.67% -3.07%
# PDF 13065 : 91206.502861
#***************************************************************************

Can you try the same method of running? I’m also surprised by our difference in the scale variation

Cheers,

Olivier

> On Nov 6, 2017, at 20:08, Kenneth Long <email address hidden> wrote:
>
> New question #660414 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/660414
>
> Hi experts,
>
> I'm generating a simple process (p p > w+) to test the reweighting to many PDFs with v2.6.0. My input cards are in [1].
>
> I then call the systematics program as
>
> pdfsets="292200,303600,292600@0,305800,315000@0,"
> pdfsets+="13100,13163@0,13167,13000@0,13065@0,"
> pdfsets+="13069,13200@0,25200@0,25300@0,25000,"
> pdfsets+="42400,42780@0,90200,91200,90400,"
> pdfsets+="91400,61100,61130,61200,61230,"
> pdfsets+="13400,82000"
> scalevars="--mur=1,2,0.5 --muf=1,2,0.5 --together=muf,mur --dyn=-1"
>
> ./bin/aMCatNLO "systematics $1 --pdf=$pdfsets $scalevars"
>
> The output I get is
>
> #***************************************************************************
> #
> # original cross-section: 106033.6152
> # scale variation: +-46.3% -55.5%
> #
> #PDF ABMP15_3_nnlo: 45793.2 +0.473% -0.473%
> #PDF PDF4LHC15_nnlo_100_pdfas: 55969.7 +1.3% -1.3%
> #PDF MMHT2014lo68cl: 51926.5 +0.713% -1.04%
> #PDF PDF4LHC15_nlo_30_pdfas: 53743.5 +1.28% -1.28%
> #PDF NNPDF30_nlo_nf_5_pdfas: 53187.3 +1.02% -1.02%
> #PDF HERAPDF20_NLO_EIG: 57731.6 +0.448% -0.49%
> #PDF CT14nlo: 54370 +1.28% -1.49%
> #PDF NNPDF31_nnlo_as_0118: 56704.3 +0.524% -0.524%
> #PDF NNPDF31_nlo_hessian_pdfas: 55194.6 +0.929% -0.929%
> #PDF HERAPDF20_NNLO_EIG: 58950.4 +0.637% -0.675%
> #PDF PDF4LHC15_nlo_100_pdfas: 53745 +1.29% -1.29%
> #PDF LUXqed_plus_PDF4LHC15_nnlo_100: 55713.6 +1.08% -1.08%
> #PDF PDF4LHC15_nnlo_30_pdfas: 55968.6 +1.24% -1.24%
> #***************************************************************************
>
> I've tried with both LHAPDF v6.1 and 6.2 and see the same thing. I also tried with p p > e+ e- and see the same effect. The weights have the same striking trend from scale specific weights (which look fine) to PDF weights. Is it possible that there is a systematic factor of 2 being lost somewhere?
>
> Thanks,
>
> Kenneth
>
> [1] https://github.com/kdlong/genproductions/tree/mg260/bin/MadGraph5_aMCatNLO/cards/examples/wplustest_5f_NLO
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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