MadGraph5_aMC@NLO

MadSpin bridge mode with multiple final states

Asked by D

I have two processes with final states that are simply the antiparticles of each other:

generate p p > su1 > b x1+
add process p p > su1~ > b~ x1-
...
decay x1+ > b~ d~ s~
decay x1- > b d s

However, apparently this is not supported, as I get this error:

InvalidCmd : The bridge mode of MadSpin does not support event files where events do not *all* share the same set of final state particles to be decayed. One workaround is to force the final cross-section manually.

How can I do this forcing? And, if possible, is there any other way around this to generate them together?

I can generate the two processes separately without a problem. However, I would like to avoid having to compute the cross sections separately, run the production again for each, and then apply weights to combine them into one sample.

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

If the two Branching ratio are detected as different, then indeed this is not supported (and is not trivial to support).
Actually, we do support such type of assymetric decay in the normal mode, but the handling might be surprising for so many user than in general they do split the sample anyway.

The issue is that since you have multiple cross-section in a single file that are all modify by their own branching ratio,
You can not keep the all the properties of the original sample (unweighted events, number of events,...)

The work-around proposed here is quite complex to setup and non tested since many years (I just tried and it is not python3 compatible). So I would not advise to use it and indeed generate separate sample.

If your two BR are identical then the situation is diffferent and this is likely just a threshold to fix to allow your process to go trough

Cheers,

Olivier

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D (devinmahon) said : 		#2

Hi Olivier,

Thanks for your quick response! Here, the BRs for the two MadSpin decays are the same (in this case, in fact, they are 1). How can I make this threshold change you mentioned?

Best,
Devin

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Launchpad Janitor (janitor) said : 		#3

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

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D (devinmahon) said : 		#4

Hi again,

I would still like to know how to do this "threshold" fix. Both decays x1+ > b~ d~ s~ and decay x1- > b d s have BRs of 1.

From the param card:

DECAY 1000024 1.000000e-08 # Wch1
      1.0e+00 3 -5 -3 -1

Please let me know if you can clarify how to do this.

Best,
Devin

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Olivier Mattelaer (olivier-mattelaer) said : 		#5

Can you send me the model? (<email address hidden> <mailto:<email address hidden>>)
I can try to take a look.

Olivier

> On 9 Feb 2024, at 18:15, D <email address hidden> wrote:
>
> x1+ > b~ d~ s~

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D (devinmahon) said : 		#6

That'd be great, thanks!

The model can be found here: https://feynrules.irmp.ucl.ac.be/wiki/RPVMSSM

Let me know if you need the full param card I'm using as well.

-Devin

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Olivier Mattelaer (olivier-mattelaer) said : 		#7

Ok not fully clean/secure
but the following patch: https://github.com/mg5amcnlo/mg5amcnlo/commit/c4827e43411e04d0dc9fa195a3e19ce829079846
does allow your specific case to go trough.

The check are relatively weak (only on the identity of the BR) so one can certainly abuse the feature and produce non sense. The warning should be enough to warn people (I hope).

Cheers,

Olivier
> On 9 Feb 2024, at 21:00, D <email address hidden> wrote:
>
> Question #708760 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/708760
>
> D posted a new comment:
> That'd be great, thanks!
>
> The model can be found here:
> https://feynrules.irmp.ucl.ac.be/wiki/RPVMSSM
>
> Let me know if you need the full param card I'm using as well.
>
> -Devin
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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D (devinmahon) said : 		#8

Thanks so much, Olivier! That seems to have done the trick!

-Devin