BSM model / MG5+Pythia not decaying SM particles

Hi Marco,

In order to allow Pythia to decay correctly the top and the Higgs,
you probably need to specify the branching ration of all top/higgs decay.
Of course, the decay with Pythia is faster but it doesn't take into account full spin correlations (which might be fine depending of your need).

If it doesn't help, my suggestion would be to contact the Pythia author (please put me in cc) such that they can indicate why this is not working.

Cheers,

Olivier

On Jun 1, 2013, at 1:31 AM, Marco Tonini <email address hidden> wrote:

> New question #230023 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/230023
>
> Hello,
> I have implemented a BSM model using FeynRules: I am interested in a signature where a top partner decays into the SM top plus the SM Higgs. I assigned to this top partner a PDG number 8880008. I have generated a process with the following sintax using MadGraph 1.5.9 (theven is the top partner):
>
> define the = theven theven~
> define q = u u~ d d~ s s~ c c~
> define qb = b b~
> define qt = t t~
>
> generate g q > the qb q, the > qt h
>
> I would like to let Pythia decay the SM top and Higgs according to their branching ratios. However this does not work properly. I can provide the log file of Pythia. The same happens also if I try to decay/shower the parton level events using Pythia externally from MadGraph.
>
> But if I specify the full decay chain already at the generation of the process, everything works fine:
>
> define w = w+ w-
> define wdecay = q l+ l- vl vl~
>
> generate g q > the qb q, (the > qt h, (qt > w qb, w > wdecay wdecay), h > b b~)
>
> but is much more time consuming. I would then like to ask you kindly a suggestion to overcome this problem. In case I can provide the corresponding parton level .lhe.gz file generated with or without the full decay chain specified.
> Thank you in advance and best regards,
> Marco
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Thanks for the answer!
I'm not sure I've understood your suggestion: where should I specify the BRs of the top and the higgs? In the UFO file created by FeynRules, the decays of the top and the higgs are fully implemented, while in Pythia I don't know where I could specify different BRs. If you mean to specify the complete decay chain already at process-generation level in MG5, this works indeed, but it is exactly the point of my question. Could you please explain in more detail your suggestion?
Thanks again four you attention,
Best regards,
Marco

Hi Marco,

> If you mean to specify the complete decay chain already at process-generation level in MG5, this works indeed, but it is exactly the point of my question. Could you please explain in more detail your suggestion?

Yes that was my suggestion. MG5 will not use this information (i.e. the branching ratio) but will transfer the information to Pythia.

Cheers,

Olivier

On Jun 3, 2013, at 4:16 PM, Marco Tonini <email address hidden> wrote:

> Question #230023 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/230023
>
> Status: Answered => Open
>
> Marco Tonini is still having a problem:
> Thanks for the answer!
> I'm not sure I've understood your suggestion: where should I specify the BRs of the top and the higgs? In the UFO file created by FeynRules, the decays of the top and the higgs are fully implemented, while in Pythia I don't know where I could specify different BRs. If you mean to specify the complete decay chain already at process-generation level in MG5, this works indeed, but it is exactly the point of my question. Could you please explain in more detail your suggestion?
> Thanks again four you attention,
> Best regards,
> Marco
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Ok, thanks! Eventually I'll try to contact the Pythia authors, too.
Thanks again,
Marco