ttH sample issue

Dear Silvia,

I will need much more information in order to help you.

1) What is the syntax that you use in MG5_aMC@NLO?

And in particular how are generated the decay of the Higgs/top?
Inside MG? via MadSpin, via an external program (Herwig?/Pythia?)

2) What are the cut on the lepton/jet/…

3) When you say that you “found” ~ 1000 events, which kind of events are you talking about,
is this parton level recored? before or after shower? or is it at reconstructed level? (if so then which detector simulation did you use).

Cheers,

Olivier

Dear Olivier,

1) the syntax I’ve used to generate events is: generate p p > t t~ h
and during the generation procedure I’ve used Pythia and Delphes.

2) the pt cut (that is the only cut) is 20 GeV for leptons, jets, b,
no cut for the other particles.

3) I mean parton level events (we’ve used only truth information) and at this level we found that
~30% of ttH events have a decay like this: H -> b + light quark. It seems strange for us,
so we would figure out if we’re making some mistakes.

Thank you very much.

Cheers,

Silvia

reply of sylvia (by direct email):
Dear Olivier,

1) the syntax I’ve used to generate events is: generate p p > t t~ h
and during the generation procedure I’ve used Pythia and Delphes.

2) the pt cut (that is the only cut) is 20 GeV for leptons, jets, b,
no cut for the other particles.

3) I mean parton level events (we’ve used only truth information) and at this level we found that
~30% of ttH events have a decay like this: H -> b + light quark. It seems strange for us,
so we would figure out if we’re making some mistakes.

Thank you very much.

Bests,
Silvia Biondi
************************************************************************************
answer:

Dear Silvia,

I can not help you with that since the decay is handle by Pythia and not by any of the MadGraph module that I know/maintain.
I would suggest then to either handle those decay internally inside MG. (either via the decay syntax, or via MadSpin) or contact the Pythia author/read the Pythia manual.

Cheers,

Olivier

Dear Olivier,

so what you're suggesting is to generate the decays inside MG, in this case I don't need
to include Pythia in the generation, right?

Just a technical question: in order to do that, do I have to specify something during
the generation procedure? I mean, I've followed instructions I found on the MG site,
do you have some other specific suggestions I can follow (commands, packages to install, etc..)?

Thank you,
cheers,

Silvia

Hi,

> so what you're suggesting is to generate the decays inside MG, in this case I don't need
> to include Pythia in the generation, right?

You still need Pythia for the shower/hadronization.

> Just a technical question: in order to do that, do I have to specify something during
> the generation procedure?

either you use the decay chain syntax:
generate p p > t t~ h, t > b l+ vl, t~ > b~ j j , h > b b~
add process p p > t t~ h, t > b j j , t~ > b~ l- vl~ , h > b b~

if you use this method, you can take a look at the following FAQ: https://answers.launchpad.net/mg5amcnlo/+faq/2442

Or you can use MadSpin (arXiv:1212.3460)
In that case you just generate:
generate p p > t t~ h
and at the question:

The following switches determine which programs are run:
 1 Run the pythia shower/hadronization: pythia=OFF
 2 Run PGS as detector simulator: pgs=OFF
 3 Run Delphes as detector simulator: delphes=OFF
 4 Decay particles with the MadSpin module: madspin=OFF
 5 Add weight to events based on coupling parameters: reweight=OFF
  Either type the switch number (1 to 5) to change its default setting,
  or set any switch explicitly (e.g. type 'madspin=ON' at the prompt)
  Type '0', 'auto', 'done' or just press enter when you are done.
 [0, 1, 2, 3, 4, 5, auto, done, pythia=ON, … ][60s to answer]

You have to set MadSpin on True, and then edit the madspin_card to specify the requested decay.

Cheers,

Olivier

On 12 Dec 2014, at 10:41, Silvia <email address hidden> wrote:

> Question #258939 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/258939
>
> Status: Answered => Open
>
> Silvia is still having a problem:
> Dear Olivier,
>
> so what you're suggesting is to generate the decays inside MG, in this case I don't need
> to include Pythia in the generation, right?
>
> Just a technical question: in order to do that, do I have to specify something during
> the generation procedure? I mean, I've followed instructions I found on the MG site,
> do you have some other specific suggestions I can follow (commands, packages to install, etc..)?
>
> Thank you,
> cheers,
>
> Silvia
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks Olivier Mattelaer, that solved my question.

Dear Olivier,

I've found the problem: I was identifying (off line) the h->bb events looking at the higgs' daughters (D1, D2),
instead of looking at the b having higgs as mother.
Now I found correct % of events.

For my personal knowledge, could you please explain me why I see this strange behavior looking at D1 and D2?
For example, I see an higgs with pdgID(D1) = 1 and pdgID(D1) = 2, or pdgID(D1) = 22 and pdgID(D1) = 5.

Thank you for your kindness.

Cheers,

Silvia

Dear Silvia,

This is actually some detail of Pythia, which I do not know enough in order to give you an answer. You can either contact the Pythia author or read the Pythia manual.

Cheers,

Olivier