MadGraph5_aMC@NLO

Counterterms for Herwig7

Asked by Andrej Saibel

Dear all,

I have a basic question:

When MG5_aMC@NLO runs in NLO mode, it also calculates the counter terms according to the parton shower used. Is it correct that the counter terms are different for the different parton showers? If so, which parton shower do I need to specify in order to produce LHE files which can be showered with Herwig7?

If one produces an LHE file with an LO process and then showers it with Pythia or Herwig, does it matter which parton shower was defined in the run_card?

Thanks a lot for your time!

Kind regards,

Andrej

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Paolo Torrielli Edit question
Solved by:
Olivier Mattelaer
Solved:
Last query:
Last reply:
Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Yes you are correct the couterterm are PS dependent and therefore you can NOT shower a sample with PY8 if the counterterm used was the one associated to PY6 or Herwig.

In the case of Herwig7, they use the same configuration as Herwig++ and therefore you can set for Herwig7, the counterterm to
HERWIGPP

Cheers,

Olivier

PS: I assigned this to paolo since he is the expert in that part of the code, to be 100% that I do not say anything wrong here.

Revision history for this message
Andrej Saibel (asaibel) said : 		#2

Hi Olivier,

thanks a lot for the answer!This is exactly what I was looking for.

@Paolo, can you comment what is the case for LO production?

If one produces an LHE file with an LO process and then showers it with Pythia or Herwig, does it matter which parton shower was defined in the run_card?

Kind regards,

Andrej

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

At LO, they are not PS counter-term and therefore you can run the parton-shower that you want on those sample.

We have two method to run LO events:
1) the one called "Madevent" which is the one you get if you do
generate p p > w+ w-
In this case, the run_card does not contains any field associated to the parton_shower.

2) the one called "aMC@LO" which is the one you get if you do
generate p p > w+ w- [QCD]
output
launch
order=LO

In that case, the run_card is the same as the one of the NLO (this is very practical to compute K-factor).
and indeed you have a field related to the parton-shower used. But it does not matter for LO run.
Now It is possible that such run as the same security as the NLO ones meaning that if you try within MG5aMC to run another parton-shower it is possible that it will be forbidden.

Cheers,

Olivier

> On 26 Jun 2019, at 12:13, Andrej Saibel <email address hidden> wrote:
>
> Question #681605 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/681605
>
> Status: Answered => Open
>
> Andrej Saibel is still having a problem:
> Hi Olivier,
>
> thanks a lot for the answer!This is exactly what I was looking for.
>
> @Paolo, can you comment what is the case for LO production?
>
> If one produces an LHE file with an LO process and then showers it with
> Pythia or Herwig, does it matter which parton shower was defined in the
> run_card?
>
> Kind regards,
>
> Andrej
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Andrej Saibel (asaibel) said : 		#4

Hi Olivier,

Thank you very much for the answer!

Kind regards,

Andrej

Revision history for this message
Andrej Saibel (asaibel) said : 		#5

Thanks Olivier Mattelaer, that solved my question.