MadGraph5_aMC@NLO

Generating off-shell events with new physics

Asked by Jay Vora

Dear Olivier,

I am executing the following generation command using the LO LQ model from here [1]:
p p > top tau j nu

However, this results in a large cross-section of contributions from SM processes. Is there a way in madgraph to ensure I only generate diagrams with an intermediate LQ while also allowing it to be off-shell?

Best,
Jay Vora

[1] https://lqnlo.hepforge.org/

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

Hi,

I guess that the question boils down to how to select a subset of the diagram (which is the FAQ that I linked to this question)
However, I might not have the exact answer to your question since you need to know very well what is gauge invariant in your model and to know exactly which diagram you want to neglect/ ....

But in short, you have three option here
1) use "unsafe" MG5aMC syntax to remove the diagram you want (unsafe in the way that we can not guarantee that the result is gauge/lorentz invariant/...)
various syntax are available here
p p > top tau j nu $$ W+ (forbidding the particle W+ to be in S-channel)
p p > l1 > top tau j nu (keeping diagram only with at least one l1 in s-channel
p p > l1 | l2 > top tau j nu (keeping diagram only with at least one l1 in s-channel or at least one l2 in s-channel
p p > top tau j nu / W+ (forbidding the particle W+ to appear --both S and T channel--)

2) write your own python function to decide to keep or not your diagram (full detail in the FAQ)

3) Use a coupling order restriction (as asked in your other thread).

Cheers,

Olivier

FAQ #3322: “How to select of subset of diagram for LO computation?”.

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Jay Vora (jvora123) said : 		#2

Thanks Olivier Mattelaer, that solved my question.