length of decay chain in madspin

Asked by Alexander Grohsjean on 2018-08-09

Dear all,

I would like to restrict my NLO sample at Madspin level to dileptonic top decays, e.g. W > e nu_e , W > mu nu_mu but also
W > tau nu_tau , where the tau decays into e/mu and the corresponding neutrinos. Specifying these different possibilities in my decay syntax I still see taus in the final state.
Should I give up as it is not possible in Madspin or is there some special trick, syntax needed?

Cheers, Alexander.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2018-08-09
Last query:
2018-08-09
Last reply:
2018-08-09

Hi,

In principle the syntax should have been
decay w+ > e+ ve
decay w+ > mu+ vm
decay w+ > ta+ vt , ta+ > e+ ve vt~
decay w+ > ta+ vt , ta+ > mu+ vm vt~

but this include a three body decay which is not supported by MadSpin in its default mode.
You can pass to a less precise mode of MadSpin (onshell or none) and then it would be possible
but at the cost of loosing at least the off-shell effect (or even the spin-correlation in the last case)

So my recomendation is to not let the tau decay within MadSpin and use taoula (or similar) for handling such decay.

Cheers,

Olivier

> On 9 Aug 2018, at 21:42, Alexander Grohsjean <email address hidden> wrote:
>
> New question #671470 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/671470
>
> Dear all,
>
> I would like to restrict my NLO sample at Madspin level to dileptonic top decays, e.g. W > e nu_e , W > mu nu_mu but also
> W > tau nu_tau , where the tau decays into e/mu and the corresponding neutrinos. Specifying these different possibilities in my decay syntax I still see taus in the final state.
> Should I give up as it is not possible in Madspin or is there some special trick, syntax needed?
>
> Cheers, Alexander.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks Olivier for the confirmation. That's what I tried! So I will stop with the tau in Madspin.