Different PDFs sets for different beams

Asked by oleh on 2018-02-20

Dear MadGraph experts,

is is possible to use different PDFs sets for different beams in MadGraph?

I did not managed to find a default flag, but maybe one can modify some internal MadGraph files ?

Thank you!

Cheers,
Oleh

Question information

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Solved by:
oleh
Solved:
2018-02-21
Last query:
2018-02-21
Last reply:
2018-02-21

Hi,

No this is not supported.

My typical suggestion is to use reweighting for that (in post-processing)

Cheers,

Olivier

oleh (fedkevych) said : #2

Dear Oliver,
many thanks for finding time to answer my question.

If it is possible could you please explain what do you assume by reweighting?
(my initial idea was to use a set of Nuclear PDFs together with a set of usual PDFs )
Does rewaighting mean that I have to multiply my cross section by certain nuclear modification factor?

Cheers,
Oleh

Hi,

By reweighting, I mean that you have to read the lhe file and change the weigh of each event by the following ratio:

pdf_new(x1, q1)/pdf_old(x1,q1)

in the lhe file, you have the information about x1 and q1 written inside the <mgrwgt> block.

We do not have a code for doing that automatically, but you can look at the systematics.py scripts which does similar stuff
(but on both beam actually) so the easiest is probably to hack that script to only reweight over a single pdf.

Cheers,

Olivier

> On 21 Feb 2018, at 10:07, oleh <email address hidden> wrote:
>
> Question #664700 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/664700
>
> Status: Answered => Open
>
> oleh is still having a problem:
> Dear Oliver,
> many thanks for finding time to answer my question.
>
> If it is possible could you please explain what do you assume by reweighting?
> (my initial idea was to use a set of Nuclear PDFs together with a set of usual PDFs )
> Does rewaighting mean that I have to multiply my cross section by certain nuclear modification factor?
>
> Cheers,
> Oleh
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

oleh (fedkevych) said : #4

Dear Oliver,

thank you very much.

This solved my problem.

Cheers,
Oleh