fNLO and LHE files

Asked by Hannes Jung on 2021-03-24

Dear Madgraph experts

I would like to compare predictions from fNLO (at parton level) with those obtained with MCatNLO (after showering) also at parton level. In the fNLO mode, one can select as output LHE.
Sine many analyses are implemented in Rivet, I was wondering whether one can use the fNLO lhe files and create HepMC files which can be read by Rivet directly.

Perhaps this has been already done... but I could not find any reference for it, or is there any principle problem ?

Thanks a lot in advance

Best
Hannes

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2021-03-24
Last query:
2021-03-24
Last reply:
2021-03-24

Hi,

You can not run a parton-shower on the lhef file associated to the fNLO.
So the only option would be to convert the lhef to Hepmc.
(but this invalidates most of the RIVET analysis)

However the LHEF is in a special format (version 2) which is not used very often since it contains events and counter-events and you need to make sure that events and counter-events are treated in the exact same way both at the level of the converter and at the level of the analysis.

Cheers,

Olivier

> On 24 Mar 2021, at 08:20, Hannes Jung <email address hidden> wrote:
>
> New question #696227 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/696227
>
> Dear Madgraph experts
>
> I would like to compare predictions from fNLO (at parton level) with those obtained with MCatNLO (after showering) also at parton level. In the fNLO mode, one can select as output LHE.
> Sine many analyses are implemented in Rivet, I was wondering whether one can use the fNLO lhe files and create HepMC files which can be read by Rivet directly.
>
> Perhaps this has been already done... but I could not find any reference for it, or is there any principle problem ?
>
> Thanks a lot in advance
>
> Best
> Hannes
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hannes Jung (hannes.jung) said : #2

Dear Olivier
thanks a lot for this very fast reply.

Yes, sure,... fNLO cannot be showered... I just want them as they come, without anything else.

Do you have any reference at hand describing the issue of counter events ? Is it enough to add properly the weights depending on the partonic final state ?

thanks again
Cheers
Hannes

I do not know,
Maybe the lhef v2 paper discuss that but not sure.
But the idea is that one event group should be handle in a single block and can not be separated.

Olivier

> On 24 Mar 2021, at 08:45, Hannes Jung <email address hidden> wrote:
>
> Question #696227 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/696227
>
> Status: Answered => Open
>
> Hannes Jung is still having a problem:
> Dear Olivier
> thanks a lot for this very fast reply.
>
> Yes, sure,... fNLO cannot be showered... I just want them as they come,
> without anything else.
>
> Do you have any reference at hand describing the issue of counter events
> ? Is it enough to add properly the weights depending on the partonic
> final state ?
>
> thanks again
> Cheers
> Hannes
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hannes Jung (hannes.jung) said : #4

Thanks Olivier Mattelaer, that solved my question.