lhe files for pythia8 analysis

Dear Juhi,

The file events.lhe corresponds to weighted events (actually they are partially unweighted) at parton level.
it can be used to be showered by pyhia6/pythia8/HW7/…

The file unweighted_events.lhe corresponds to unweighted events. Those events are a sub-sample of events.lhe
it can be used to be showered by pyhia6/pythia8/HW7/…

All the events of unweighted_events.lhe are in events.lhe (but not the opposite and not with the same weight).
The precision of the various distribution is typically predicted by events.lhe and unweighted_events.lhe is in first approximation equivalent.
(events.lhe should be slightly more precise).
Showering unweighted_events.lhe is therefore much faster (since it has less events).
Therefore unweighted_events.lhe is typically used since
1) The number of events is smaller -> leading to faster running time
2) The analysis is easier since all the events have the same weight (so in principle you do not have to worry abut those)

The tag_1_pythia_lhe correspond to events after pardon-shower and detector simulation (a very basic one: just a cone algorithm).
In particular it use a cone algorithm to reconstruct the jets. The main purpose of this file is to be able to easily make plots/ fast analysis.
Since it is already at detector level, this file can not be showered. (No shower will allow you to do that since the events do not conserve energy momenta due to the
soft jet removed by the jet-clustering.

Cheers,

Olivier

> On Feb 1, 2016, at 11:51, Juhi Dutta <email address hidden> wrote:
>
> Question #284263 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/284263
>
> Summary changed to:
> lhe files for pythia8 analysis
>
> Description changed to:
> Dear MG5 experts,
>
> I have generated a process p p > t t~ with 0,1,2 jets involving the mlm
> matching procedure. I want to extract the lhe file with the matching
> done to use it in pythia8 for analysis . Which one of the lhe files
> among unweighted_events.lhe, events.lhe or tag_1_pythia_lhe.gz do I use?
> Which one of these lhe files can be used for a separate analysis with
> pythia8?
>
> Does the final lhe file generated during the pythia showering in
> madgraph has the matched set of events? In which case if I analyse it
> in pythia8 I will not have to perform matching. Is that the case?
>
> It would be very helpful if you kindly advise me in this regard.
>
> Thanks & Regards,
>
> Juhi Dutta
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hello,

Thank you for the very clear and detailed response Olivier ! So in principle tag_1_pythia.lhe file has the reconstructed objects and at this stage with the shower done the matching has been performed. Since the detector simulation is a very basic one, is that why it is warned against using in detector studies? I was thinking whether it is correct to use this matched showered pythia file for further analysis in pythia8 without showering.

Thanks & Regards,

Juhi Dutta

Hi,

> Since
> the detector simulation is a very basic one, is that why it is warned
> against using in detector studies?

Yes,that’s the main reason. Basically any detector studies starts by defining a jet algorithm (the most popular is anti-kt)
So in this file this is already done with a cone algorithm. In top of that no acceptance is performed.
One someone report that some smearing are applied but I doubt about it but I did not check.

> I was thinking whether it is
> correct to use this matched showered pythia file for further analysis in
> pythia8 without showering.

This sounds a bad idea to me. But I’m sure that if you succeed to import the file, they are ways of doing consistent stuff.
But they are so many ways to screw stuff in this method that I should discourage you of doing that.

Cheers,

Oliver

> On Feb 1, 2016, at 14:42, Juhi Dutta <email address hidden> wrote:
>
> Question #284263 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/284263
>
> Status: Answered => Open
>
> Juhi Dutta is still having a problem:
> Hello,
>
> Thank you for the very clear and detailed response Olivier ! So in
> principle tag_1_pythia.lhe file has the reconstructed objects and at
> this stage with the shower done the matching has been performed. Since
> the detector simulation is a very basic one, is that why it is warned
> against using in detector studies? I was thinking whether it is
> correct to use this matched showered pythia file for further analysis in
> pythia8 without showering.
>
> Thanks & Regards,
>
> Juhi Dutta
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi,

Thanks for the reply! Ok so it isn't probably a good idea to use the lhe from pythia.

pythia 8 takes in hepmc inputs. Is there a way that can be obtained using the stdhep file?

Thanks & Regards,

Juhi Dutta

Thanks Olivier Mattelaer, that solved my question.

Dear Olivier,

Sorry for hijacking this thread - but I believe my question is connected to this one

I want to produce gg->h->4l at NLO, showered with pythia8. I would like to do the showering outside of the mg5_aMC@NLO framework (which does not sounds like the simplest way of doing it, but it makes other things somewhat easier for me). Is it possible ?

My understanding is that when I put shower=OFF in a NLO run the subtraction terms are still present, and they would depend on the parton shower for which they have been computed. Am I correct ? And how do I tell mg5_aMC@NLO to compute these terms for pythia8 instead of HW7 ?

Thanks !
Kind regards

Cyril

Hi Cyril,

>I want to produce gg->h->4l at NLO, showered with pythia8. I would like to do the showering outside of the mg5_aMC@NLO
>framework (which does not sounds like the simplest way of doing it, but it makes other things somewhat easier for me). Is it possible ?

Yes

>My understanding is that when I put shower=OFF in a NLO run the subtraction terms are still present, and they would depend on
>the parton shower for which they have been computed. Am I correct ?

Yes

>And how do I tell mg5_aMC@NLO to compute these terms for pythia8 instead of HW7 ?

This is specified in the run_card.dat via the parameter "parton_shower"
in your case, you have to set it on PYTHIA8

Cheers,

Olivier