MadGraph5_aMC@NLO

how to force a particle stable with pythia-pgs (or plot intermediate particles)

Asked by marco zaro

Hi,
I am looking at MLM merged higgs events in gluon fusion (using V2.4.2).

import model heft
generate p p > h
add process p p > h j
output gg_h_heft_1j

(default run and param card)

I would like to plot the Higgs pT with Pythia + MadAnalysis tools.
I have edited the pythia card in order not to decay the Higgs, adding
 ! higgs stable
       MDCY(C25,1)=0

In the plot Card I have added

Higgs 25

and modified the pt range from 0 -> 200, with bins of 4 gev

In the plots i notice two strange issues
1) there are more than half events with no higgs, the rest with one
2) the higgs pt is very soft, like if it were coming only from the 0-jet sample. In contrast the first jet pt looks totally reasonable

What am I doing wrong?
And how can I plot the Higgs pT for the merged sample?

I have also tried not to force the higgs stable in the pythia_card, but the plots do not change...

Thanks for your help!

Cheers,

Marco

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

Hi Marco,

I guess that the problem is that the stdhep to lhef converter merge the Higgs in the jets in some case.
Which makes this effects on the plot.

Probably better to make the plot with MA5 using directly the stdhep input.

Cheers,

Olivier

Revision history for this message
marco zaro (marco-zaro) said : 		#2

Thanks Olivier Mattelaer, that solved my question.

Revision history for this message
marco zaro (marco-zaro) said : 		#3

Ciao Olivier,
thanks,
another very trivial thing i have discovered, is the plot_decayed variable in the plot card.
If it is set to yes, then plots become meaningful without having to add the MDCY to the pythia card.
Thanks a lot!
Cheers,

Marco
On 21 Jul 2016, at 06:22, Olivier Mattelaer <email address hidden> wrote:

> Your question #298259 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/298259
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Hi Marco,
>
> I guess that the problem is that the stdhep to lhef converter merge the Higgs in the jets in some case.
> Which makes this effects on the plot.
>
> Probably better to make the plot with MA5 using directly the stdhep
> input.
>
> Cheers,
>
> Olivier
>
> --
> If this answers your question, please go to the following page to let us
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> https://answers.launchpad.net/mg5amcnlo/+question/298259/+confirm?answer_id=0
>
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