MadGraph5_aMC@NLO

Excluding specify decay chains

Asked by Ben Scully

Is there a way to exclude specific decay chains in an interaction? I am running an interaction where an electron collides with a stationary target nucleus which results in it putting off a photon which decays into an electron positron pair. I have been using a top quark as my stationary target due to it's much higher mass than the electron (the beam energy is only 30 MeV). I also set the top quark mass to be 1e3MeV but this appears to cause negligible change.

To do this I use:
    e- t > e- e+ e- t /h z

I exclude the h and z because I am only interested in interactions via photons.
Extra information: I have been using the model sm full for this. It only works if I set the sde_strategy = 1, and set the following cuts to be ptl = 0, etal = 5, drll = 0.

My issue is that there are diagrams produced in which the photon is emitted off of the top quark rather than the electron which I do not want. Is there a way to exclude specific decays when I generate the process,
      e.g. by doing e- t > e- e+ e- t /h z (t > t a) -- I know this doesn't work but something along these lines.

Apologies if there is anything wrong with the way I phrased the question, I am new to using MadGraph and am happy to take any advice on how I can approach this.

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

I guess the best here is to edit the model to remove the t t~ a photon interaction.

Otherwise, you can check the FAQ on how to remove diagram.

Cheers,

Olivier

> On 16 Jan 2024, at 19:50, Ben Scully <email address hidden> wrote:
>
> New question #709013 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/709013
>
> Is there a way to exclude specific decay chains in an interaction? I am running an interaction where an electron collides with a stationary target nucleus which results in it putting off a photon which decays into an electron positron pair. I have been using a top quark as my stationary target due to it's much higher mass than the electron (the beam energy is only 30 MeV). I also set the top quark mass to be 1e3MeV but this appears to cause negligible change.
>
> To do this I use:
> e- t > e- e+ e- t /h z
>
> I exclude the h and z because I am only interested in interactions via photons.
> Extra information: I have been using the model sm full for this. It only works if I set the sde_strategy = 1, and set the following cuts to be ptl = 0, etal = 5, drll = 0.
>
> My issue is that there are diagrams produced in which the photon is emitted off of the top quark rather than the electron which I do not want. Is there a way to exclude specific decays when I generate the process,
> e.g. by doing e- t > e- e+ e- t /h z (t > t a) -- I know this doesn't work but something along these lines.
>
> Apologies if there is anything wrong with the way I phrased the question, I am new to using MadGraph and am happy to take any advice on how I can approach this.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Ben Scully (ben-scully13) said : 		#2

Thanks Olivier Mattelaer, that solved my question.