Missing PDF variation (Systematics) for LO Process

Asked by Richard Ruiz on 2019-08-21

Hi Folks,

I am trying to extract the PDF variation for a loop-induced process using the CT14qed_inc_proton PDF set (lhaid=13400, 31 members). Unfortunately, mg5 Systematics is telling me that it is not possible. To clarify, this is also an issue for
CT14qed_proton (lhaid=13300) but *not*
CT14nlo (lhaid=13100, 57 members),
NNPDF23_nlo_as_0118_qed (lhaid=244600, 101 members), or
MSTW2008lo68cl (lhaid=21000, 41 members).

I am wondering if this is an issue with Systematics in mg5 or a problem with the PDF sets themselves and any input would be very much appreciated.

Best Wishes,
Richard

INFO: #***************************************************************************
#
# original cross-section: 14.076
# scale variation: +28.4% -22%
# central scheme variation: +16.3% -3.12e-09%
# PDF variation: missing combination

For, say, MSTW2008lo68cl (lhaid=21000, 41 members) I get:
INFO: #***************************************************************************
#
# original cross-section: 20.348
# scale variation: +29.3% -22.1%
# central scheme variation: +22.2% -8.19e-10%
# PDF variation: +1.06% -1.79%

The above can be reproduced with the following:
generate g g > h [QCD]
launch
set lhc 14
set nevents 400
set pdlabel lhapdf
set lhaid 13400
set no_parton_cut
done

launch
set lhaid 21000
done

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2019-08-21
Last query:
2019-08-21
Last reply:
2019-08-21

Hi,

My guess is that the method to return the uncertainty is not implemented within lhapdf.
You should have the individual cross-section for each PDF set, but since lhapdf does not know how to convert that in term of percent, we do not know either...

I can not test your script since your pdfset is not supported by lhapdf 6.1.6

Cheers,

Olivier

> On 21 Aug 2019, at 12:43, Richard Ruiz <email address hidden> wrote:
>
> New question #683125 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/683125
>
> Hi Folks,
>
> I am trying to extract the PDF variation for a loop-induced process using the CT14qed_inc_proton PDF set (lhaid=13400, 31 members). Unfortunately, mg5 Systematics is telling me that it is not possible. To clarify, this is also an issue for
> CT14qed_proton (lhaid=13300) but *not*
> CT14nlo (lhaid=13100, 57 members),
> NNPDF23_nlo_as_0118_qed (lhaid=244600, 101 members), or
> MSTW2008lo68cl (lhaid=21000, 41 members).
>
> I am wondering if this is an issue with Systematics in mg5 or a problem with the PDF sets themselves and any input would be very much appreciated.
>
> Best Wishes,
> Richard
>
> INFO: #***************************************************************************
> #
> # original cross-section: 14.076
> # scale variation: +28.4% -22%
> # central scheme variation: +16.3% -3.12e-09%
> # PDF variation: missing combination
>
> For, say, MSTW2008lo68cl (lhaid=21000, 41 members) I get:
> INFO: #***************************************************************************
> #
> # original cross-section: 20.348
> # scale variation: +29.3% -22.1%
> # central scheme variation: +22.2% -8.19e-10%
> # PDF variation: +1.06% -1.79%
>
> The above can be reproduced with the following:
> generate g g > h [QCD]
> launch
> set lhc 14
> set nevents 400
> set pdlabel lhapdf
> set lhaid 13400
> set no_parton_cut
> done
>
> launch
> set lhaid 21000
> done
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Richard Ruiz (rruiz) said : #2

Hi Olivier,

Thanks for looking into this so quickly. According to LHAPDF, the relevant CT14 PDFs are included in 6.1.6:
https://lhapdf.hepforge.org/downloads?f=pdfsets//6.1.6

Indeed the numbers I posted above used mg5amc's internal installation of LHAPDF (6.1.6)

Let me know if there is more I can do to help with this.

best,
richard

Looks like the way to compute such error is missing within the pdf sets

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________________________________
From: <email address hidden> <email address hidden> on behalf of Richard Ruiz <email address hidden>
Sent: Wednesday, August 21, 2019 1:42:35 PM
To: Olivier Mattelaer <email address hidden>
Subject: Re: [Question #683125]: Missing PDF variation (Systematics) for LO Process

Question #683125 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/683125

    Status: Answered => Open

Richard Ruiz is still having a problem:
Hi Olivier,

Thanks for looking into this so quickly. According to LHAPDF, the relevant CT14 PDFs are included in 6.1.6:
https://lhapdf.hepforge.org/downloads?f=pdfsets//6.1.6

Indeed the numbers I posted above used mg5amc's internal installation of
LHAPDF (6.1.6)

Let me know if there is more I can do to help with this.

best,
richard

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

Richard Ruiz (rruiz) said : #4

Hi Olivier,

Thanks for helping with this. Indeed, looks like the CT14qed_inc_proton PDF set is missing the lines:
ErrorType: ...
ErrorConfLevel: ...

in the CT14qed_inc_proton.info file. I will update this post once the CTEQ/CT collaboration confirms the missing relevant entries.

best,
richard

Richard Ruiz (rruiz) said : #5

Thanks Olivier Mattelaer, that solved my question.