Where in the code are PDFs defined?

Asked by Radha Mastandrea on 2021-04-21

I am curious as to where in the code I can find the exact definition of the parton distribution functions that MadGraph is using for event weighing? I see from this webpage (https://www.niu.edu/spmartin/madgraph/madtutor.html) that MadGraph uses the " CTEQ6L1 set of PDFs" but can't find where it's written out.

I'm asking because I defined a multiparticle n = g u d u~ d~, and it seems like the PDF for the multiparticle are basically equivalent to a proton's, but I would like to customize this.

Thank you!

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Hi,

If you want to use neutron PDF, you need setup the beam property as needed in the run_card.dat
when the code propose you to edit the run_card.dat

> Do you want to edit a card (press enter to bypass editing)?
> /------------------------------------------------------------\
> | 1. param : param_card.dat |
> | 2. run : run_card.dat |
> \------------------------------------------------------------/
> you can also
> - enter the path to a valid card or banner.
> - use the 'set' command to modify a parameter directly.
> The set option works only for param_card and run_card.
> Type 'help set' for more information on this command.
> - call an external program (ASperGE/MadWidth/...).
> Type 'help' for the list of available command
> [0, done, 1, param, 2, run, 3, plot, enter path][90s to answer]

you can start by replying by "update ion_pdf"

> >update ion_pdf
> INFO: add optional block ion_pdf to the run_card

Then you can open the run_card and will see the following parameter in your run_card.
And then you can set it as needed:

> #*********************************************************************
> # Heavy ion PDF / rescaling of PDF *
> #*********************************************************************
> 1 = nb_proton1 # number of proton for the first beam
> 0 = nb_neutron1 # number of neutron for the first beam
> -1.0 = mass_ion1 # mass of the heavy ion (first beam)
> # Note that seting differently the two beams only work if you use
> # group_subprocess=False when generating your matrix-element
> 1 = nb_proton2 # number of proton for the second beam
> 0 = nb_neutron2 # number of neutron for the second beam
> -1.0 = mass_ion2 # mass of the heavy ion (second beam)

To answer your question, the code is in Source/PDF/
the impact of that optional block is mainly impacting pdg2pdf.g and pdg2pdf_lhapdf6.f

Cheers,

Olivier

> On 21 Apr 2021, at 16:15, Radha Mastandrea <email address hidden> wrote:
>
> New question #696671 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/696671
>
> I am curious as to where in the code I can find the exact definition of the parton distribution functions that MadGraph is using for event weighing? I see from this webpage (https://www.niu.edu/spmartin/madgraph/madtutor.html) that MadGraph uses the " CTEQ6L1 set of PDFs" but can't find where it's written out.
>
> I'm asking because I defined a multiparticle n = g u d u~ d~, and it seems like the PDF for the multiparticle are basically equivalent to a proton's, but I would like to customize this.
>
> Thank you!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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