MadAnalysis 5

fastjet : stable vs unstable taus

Asked by Ioannis Tsinikos

Dear MA5 experts,

I am working on a pp->ttH process. I am using aMC@NLO to generate LO events at 8 TeV. I use PYTHIA8 in the aMC@NLO framework for shower/hadronization. I decay in PYTHIA8 the H->WW and all the W's leptonically (e, mu, tau). In the shower_card.dat the default tau behavior is to decay. So I get the events_PYTHIA8_hepmc.gz file. I read this with ./bin/ma5 -H, I plot NAPID and indeed there are no final state taus as expected. Then in the MA5 framework I apply the fastjet algorithm in this hepmc file. I use antikt, R=0.5, ktmin=25 GeV and I leave the rest as default. This gives me the lhco event file. I read this with ./bin/ma5 -R, I plot NAPID and now there are final state taus. I look at the lhco file and indeed there are particles of type 3, which, according to the lhco header, correspond to hadronically decaying taus. I do not understand why they appear.

I repeat the whole procedure by setting the taus stable in the shower_card.dat for PYTHIA8. I get a new hepmc file. I read it and now there are, as expected, final state taus. Furthermore the number of taus is the same with the number of electrons and of muons, which is also expected. I apply the fastjet algorithm like before to the new hepmc file and I read the new lhco file. Now surprisingly there are no final state taus.

Is this behavior normal? Am I missing something in the fastsim settings in MA5?

Thank you in advance,
Ioannis

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Benjamin Fuks
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Best Benjamin Fuks (fuks) said : 		#1

Dear Ioannis,

This behaviour is normal as the fastsim procedure assumed that all unstable particles have been decayed. If you really meed those undecayed taus, I can show you how to modify the code.

Cheers,

Benjamin

PS: my internet connectivity will be limited until April 6th so that there may be some delays with my answers...

On 26 Mar 2015, at 02:21 , Ioannis Tsinikos <email address hidden> wrote:

> New question #264162 on MadAnalysis 5:
> https://answers.launchpad.net/madanalysis5/+question/264162
>
> Dear MA5 experts,
>
> I am working on a pp->ttH process. I am using aMC@NLO to generate LO events at 8 TeV. I use PYTHIA8 in the aMC@NLO framework for shower/hadronization. I decay in PYTHIA8 the H->WW and all the W's leptonically (e, mu, tau). In the shower_card.dat the default tau behavior is to decay. So I get the events_PYTHIA8_hepmc.gz file. I read this with ./bin/ma5 -H, I plot NAPID and indeed there are no final state taus as expected. Then in the MA5 framework I apply the fastjet algorithm in this hepmc file. I use antikt, R=0.5, ktmin=25 GeV and I leave the rest as default. This gives me the lhco event file. I read this with ./bin/ma5 -R, I plot NAPID and now there are final state taus. I look at the lhco file and indeed there are particles of type 3, which, according to the lhco header, correspond to hadronically decaying taus. I do not understand why they appear.
>
> I repeat the whole procedure by setting the taus stable in the shower_card.dat for PYTHIA8. I get a new hepmc file. I read it and now there are, as expected, final state taus. Furthermore the number of taus is the same with the number of electrons and of muons, which is also expected. I apply the fastjet algorithm like before to the new hepmc file and I read the new lhco file. Now surprisingly there are no final state taus.
>
> Is this behavior normal? Am I missing something in the fastsim settings in MA5?
>
> Thank you in advance,
> Ioannis
>
> --
> You received this question notification because you are an answer
> contact for MadAnalysis 5.

Revision history for this message
Ioannis Tsinikos (ioannis-tsinikos) said : 		#2

Dear Benjamin,

thank you for your prompt answer. So I understand that if I set them stable, fastsim practically ignores them and that is why they do not appear. I am not interested in undecayed taus. Concerning the first case where I let them decay in the shower, I assume that the taus I see after fastsim are actually tau-jets. If this is the case your answer solves my problem.

Best,
Ioannis

Revision history for this message
Ioannis Tsinikos (ioannis-tsinikos) said : 		#3

Thanks Benjamin Fuks, that solved my question.

Revision history for this message
Benjamin Fuks (fuks) said : 		#4

Hi,

Actually, they are accounted for in the jet collection if they are not decayed. When they are decayed, the taus you observe are indeed tau jets.

Cheers,

Benjamin

On 26 Mar 2015, at 08:26 , Ioannis Tsinikos <email address hidden> wrote:

> Question #264162 on MadAnalysis 5 changed:
> https://answers.launchpad.net/madanalysis5/+question/264162
>
> Status: Answered => Solved
>
> Ioannis Tsinikos confirmed that the question is solved:
> Dear Benjamin,
>
> thank you for your prompt answer. So I understand that if I set them
> stable, fastsim practically ignores them and that is why they do not
> appear. I am not interested in undecayed taus. Concerning the first case
> where I let them decay in the shower, I assume that the taus I see after
> fastsim are actually tau-jets. If this is the case your answer solves my
> problem.
>
> Best,
> Ioannis
>
> --
> You received this question notification because you are an answer
> contact for MadAnalysis 5.

Revision history for this message
Ioannis Tsinikos (ioannis-tsinikos) said : 		#5

Dear Benjamin,

a ok, this clarifies even better the issue.

Thanks again,
Ioannis