# Bias in reweighted cross sections for NLO production with systematics

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=

pdfsets+

pdfsets+

pdfsets+

pdfsets+

pdfsets+

scalevars=

./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_

#PDF MMHT2014lo68cl: 51926.5 +0.713% -1.04%

#PDF PDF4LHC15_

#PDF NNPDF30_

#PDF HERAPDF20_NLO_EIG: 57731.6 +0.448% -0.49%

#PDF CT14nlo: 54370 +1.28% -1.49%

#PDF NNPDF31_

#PDF NNPDF31_

#PDF HERAPDF20_NNLO_EIG: 58950.4 +0.637% -0.675%

#PDF PDF4LHC15_

#PDF LUXqed_

#PDF PDF4LHC15_

#******

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

## Question information

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- English Edit question

- Status:
- Answered

- Assignee:
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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=

and get the following numbers which are much more reasonable.

INFO: #******

#

# original cross-section: 83570.9312275

# scale variation: +12.3% -13.2%

#

#PDF NNPDF30_

#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:/

>

> 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=

> pdfsets+

> pdfsets+

> pdfsets+

> pdfsets+

> pdfsets+

> scalevars=

>

> ./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_

> #PDF MMHT2014lo68cl: 51926.5 +0.713% -1.04%

> #PDF PDF4LHC15_

> #PDF NNPDF30_

> #PDF HERAPDF20_NLO_EIG: 57731.6 +0.448% -0.49%

> #PDF CT14nlo: 54370 +1.28% -1.49%

> #PDF NNPDF31_

> #PDF NNPDF31_

> #PDF HERAPDF20_NNLO_EIG: 58950.4 +0.637% -0.675%

> #PDF PDF4LHC15_

> #PDF LUXqed_

> #PDF PDF4LHC15_

> #******

>

> 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:/

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

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