MadGraph5_aMC@NLO

Removing unwanted diagrams

Asked by Abner Soffer

Hello. I would like to get an approximate cross section for p p > W > tau nu H (in the SM) after removing a diagram (specifically, the one in which the H is radiated directly off the W).

I see that there is a way to remove diagrams in https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15, but it seems rather complicated, and I'd rather just remove diagrams by number. An error of O(1) doesn't matter, and neither does the accuracy of the simulated events - I just need an approximate cross section.

I also see in the results.html file that there is a cross section for each individual graph. Maybe this is just what I need, but I don't understand what the naming convention G1.5 etc. means. Also, this table contains 5 graphs while in the postscript file there are only 2 diagrams. So again, the correspondence b/w the cross sections in the table and the diagrams isn't clear to me.

What should I do?

Thanks,
Abi

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

HI,

You can also directly edit all the matrix.f files and set the corresponding amplitude to 0.
In your case this sounds simple enough.

Cheers,

Olivier

PS: another method here is to remove such interaction from the UFO model
PPS: If such computation breaks gauge invariance, your result will not be lorentz invariant as well and from there weird stuff can happen.

> On 14 Aug 2019, at 21:47, Abner Soffer <email address hidden> wrote:
>
> New question #682901 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/682901
>
> Hello. I would like to get an approximate cross section for p p > W > tau nu H (in the SM) after removing a diagram (specifically, the one in which the H is radiated directly off the W).
>
> I see that there is a way to remove diagrams in https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15, but it seems rather complicated, and I'd rather just remove diagrams by number. An error of O(1) doesn't matter, and neither does the accuracy of the simulated events - I just need an approximate cross section.
>
> I also see in the results.html file that there is a cross section for each individual graph. Maybe this is just what I need, but I don't understand what the naming convention G1.5 etc. means. Also, this table contains 5 graphs while in the postscript file there are only 2 diagrams. So again, the correspondence b/w the cross sections in the table and the diagrams isn't clear to me.
>
> What should I do?
>
> Thanks,
> Abi
>
>
> --
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