MadGraph5_aMC@NLO

How to discern which beam (side) PDF is evaluated.

Asked by Karel Cerny

Dear experts,

I would like to ask you a favour.

For the purposes of my study I need to plug a new (proton) PDF to MadGraph. The thing is that I deal with
another two variables the PDFs depend on. I introduced a number of hacks I used to make in various MC
codes to read my PDF. The last step I am stuck with is to actually decide which beam is being evaluated.

What I hope I have done correctly is loading the parton arrays filled in fdist subroutine in pdf.f

Now I would need to know on which side I am actually on. I tried to look for variables in the available common blocks
but I failed to understand and unwind the code to this point.

I do not know whether I am not reinventing a wheel and the above described things are easily available in MG and that
my plea is not too vaguely described. I will be very grateful for any piece of advice.

With kind regards, Karel

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

You have the function:
double precision function pdg2pdf(ih,ipdg,beamid,x,xmu)
where you have the information of the beamid.
Now due to symmetry and optimisation this information might not be the real one.

So I would advise to run with the following flag
"set group_subprocesses False"

Cheers,

Olivier

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