MadGraph5_aMC@NLO

Unweighted events and gridpacks

Asked by Adarsh Pyarelal

When I generate events using the gridpack method, I obtain a file called events.lhe.gz. Are these weighted or unweighted events? If I wanted to replicate the MadEvent->Pythia->Delphes pipeline, would I call Pythia on the events.lhe.gz file or would I have to do an 'unweighting' procedure first?

I tried making a subfolder named Events/run_01 in the directory of the original process I had made the gridpack for (top pair production with fully leptonic decay chain), placed the events.lhe.gz files in thkand ran ./bin/madevent pythia run_01. It did not work at first. But then I renamed events.lhe.gz to unweighted_events.lhe.gz and it worked. But I am not sure if that is the right thing to do, or if I would have to do a manual unweighting of the events first.

I would be grateful if you could clarify this for me!

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

Hi,

Yes those events are indeed unweighted.
In any case pythia can handle both weighted and unweighted sample.

Cheers,

Olivier

> On Mar 16, 2016, at 01:42, Adarsh Pyarelal <email address hidden> wrote:
>
> New question #288699 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/288699
>
> When I generate events using the gridpack method, I obtain a file called events.lhe.gz. Are these weighted or unweighted events? If I wanted to replicate the MadEvent->Pythia->Delphes pipeline, would I call Pythia on the events.lhe.gz file or would I have to do an 'unweighting' procedure first?
>
> I tried making a subfolder named Events/run_01 in the directory of the original process I had made the gridpack for (top pair production with fully leptonic decay chain), placed the events.lhe.gz files in thkand ran ./bin/madevent pythia run_01. It did not work at first. But then I renamed events.lhe.gz to unweighted_events.lhe.gz and it worked. But I am not sure if that is the right thing to do, or if I would have to do a manual unweighting of the events first.
>
> I would be grateful if you could clarify this for me!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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Adarsh Pyarelal (adarsh-pyarelal) said : 		#2

Thanks Olivier Mattelaer, that solved my question.

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Eric (e-r-i-c) said : 		#3

Hi,

it seems that either the bin/compile script does not compile all the binaries/libraries needed for pythia or madevent wants to recompile the source when calling bin/madevent pythia in the gridpack. (Is this intended or is it a bug?)

However, if you do NOT call bin/clean4grid, you can replicate the MadEvent->Pythia->Delphes chain by simply running
  bin/madevent pythia GridRun_1
in the madevent folder of the gridpack (but before that, you still have to copy the events.lhe.gz to madevent/Events/GridRun_1/unweighted_events.lhe.gz)

Cheers,

Eric

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Olivier Mattelaer (olivier-mattelaer) said : 		#4

Hi Eric,

Gridpack are not suppose to run pythia at all (this is by design).
So I'm not surprise that you face some weird behavior when doing this (potentially dangerous stuff).

Cheers,

Olivier