MadGraph5_aMC@NLO

NLO VBF Higgs production

Asked by BruceLee

Hi
     I was trying to generate the VBF Higgs production @ NLO QCD with Madgraph5_aMC@NLO. But I found there were no pen and box diagrams in the virtual corrections, but only the vertex corrections, i.e. there is no exchanged virtual gluon between the two different fermion lines. While when I used FeynArts to produce the same process, I can got these diagrams. Why?

Thanks

Bruce

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
marco zaro Edit question
Solved by:
Olivier Mattelaer
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Last reply:
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Those are pentagons diagrams and are not "pure" QCD corrections. (and actually quite small)
Those contributions are actually include if you use the 3.0.1 version of MG5aMC which is still in beta.

Cheers,

Olivier

> On 15 Mar 2019, at 10:02, BruceLee <email address hidden> wrote:
>
> New question #679220 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/679220
>
> Hi
> I was trying to generate the VBF Higgs production @ NLO QCD with Madgraph5_aMC@NLO. But I found there were no pen and box diagrams in the virtual corrections, but only the vertex corrections, i.e. there is no exchanged virtual gluon between the two different fermion lines. While when I used FeynArts to produce the same process, I can got these diagrams. Why?
>
> Thanks
>
> Bruce
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
marco zaro (marco-zaro) said : 		#2

Hi,
Olivier answered already. You can get those corrections by using the same syntax (generate p p > h j j $$w+ w- z [QCD]) with 3.0.1.
Still, I am not sure that you can now forbid s-channels, you may need to keep those as well (which will be eventually suppressed by the VBF cuts)
Note that pentagons are !=0 only in those partonic processes which feature two diagrams at LO (so with identical quarks or with both W and Z fusion diagrams). In those cases they are negligible (see https://arxiv.org/pdf/0710.4749.pdf, look at delta_QCD^nondiag in tables 1-2)

Note also that you may need to load one of the EW capable models (loop_qcd_qed_sm_XXX) if you use 3.0.1

Ciao,
Marco

Revision history for this message
BruceLee (brucelee403) said : 		#3

Thanks Olivier Mattelaer, that solved my question.

Revision history for this message
BruceLee (brucelee403) said : 		#4

Thanks marco zaro too, that solved my question.