MadGraph5_aMC@NLO

discrepancy in cross-sections

Asked by maria hoffmann

Dear MadGraphers,

I use the heft model to simulate ggF of a 125 GeV Higgs with the syntax p p > h. From the LHC yellow book I expect a value around 19 pb at sqrt(s)=8 TeV. However, what I obtain is ~7 pb. Do you know why this discrepancy appears? I did not modify any kinematical cuts. Furthermore, is the raw filter efficiency accessible, or can it only be obtained through the effective cross-section MadGraph provides at the end of a run?

Thanks in advance

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Olivier Mattelaer
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Dear Maria,

> From the LHC yellow book I expect a value around 19 pb at sqrt(s)=8 TeV. However, what I obtain is ~7 pb.

I guess that this 19pb is a NLO (or even NNLO) results. This computation has an extremely large K-factor since at tree-level, the higgs does’t have any PT, going to NLO allows to have much more phase-space which is linked to a large K-factor.

> Furthermore, is the raw filter efficiency accessible, or can it only be obtained through the effective cross-section MadGraph provides at the end of a run?

I don’t understand what you mean by raw filter efficiency.

Cheers,

Olivier

On Mar 4, 2014, at 9:11 AM, maria hoffmann <email address hidden> wrote:

> New question #244954 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/244954
>
> Dear MadGraphers,
>
> I use the heft model to simulate ggF of a 125 GeV Higgs with the syntax p p > h. From the LHC yellow book I expect a value around 19 pb at sqrt(s)=8 TeV. However, what I obtain is ~7 pb. Do you know why this discrepancy appears? I did not modify any kinematical cuts. Furthermore, is the raw filter efficiency accessible, or can it only be obtained through the effective cross-section MadGraph provides at the end of a run?
>
> Thanks in advance
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
maria hoffmann (maria-hoffmann) said : 		#2

Hi again,

By raw filter efficiency I mean the MC filter efficiency stated in %. I assume the cross-section that MadGraph provides is an effective cross-section with the filter efficiency included. (If I want to scale my distributions to NLO/NNLO I need to take this into account)

thanks

Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi Maria,

Do you have a reference which defines your MC filter efficiency. I never heard about it.
But for process at LO,MG returns the cross-section at LO after the cuts defined in the run_card.dat
If you MC filter efficiency, is the efficiency by the shower to hanble such events, this number should be provide by the shower program that you use for the shower/hadronization of the events generated by MadGraph.

Cheers,

Olivier

On Mar 4, 2014, at 10:31 AM, maria hoffmann <email address hidden> wrote:

> Question #244954 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/244954
>
> maria hoffmann posted a new comment:
> Hi again,
>
> By raw filter efficiency I mean the MC filter efficiency stated in %. I
> assume the cross-section that MadGraph provides is an effective cross-
> section with the filter efficiency included. (If I want to scale my
> distributions to NLO/NNLO I need to take this into account)
>
> thanks
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
maria hoffmann (maria-hoffmann) said : 		#4

Thanks Olivier Mattelaer, that solved my question.