MadGraph5_aMC@NLO

Rejecting some diagrams when creating events?

Asked by Boever Chris

Hi,

as I am quite a beginner with the use of madgraph, I want to ask whether it is possible to generate events while discarding some of the Feynman diagrams for the production; although it might violate gauge invariance and does not account correctly for interferences, it is still interesting for my current studies.

As an example, look at the process:
generate p p > t z j b~ $$ w+ w- , z > l+ l-
and generate a sample only using diagrams where the Z-boson would originate from WW-fusion. Having a look in the SubProcesses/P1_gq_tzbxq_z_ll directory for this specific example, I want to know if it would already be enough to delete in the configs.inc file the lines corresponding to the diagrams I do not want to include?
Otherwise I would suggest one would have to change some of the code in the matrix*.f files; if so, could you please tell me which lines would require a change?

Thanks in advance for your help.

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Modifying matrix.f is a mess and can easily lead to inconsistencies. So I would not recommend it.
The correct (even if quite technical) method is to create a diagram filtering of the diagram:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15

This might requires a bit of time to understand all the structure of the diagram.
But this would be easier (and much cleaner) at the end of the day.

Cheers,

Olivier

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