MadGraph5_aMC@NLO

Plot of cross section vc polarization.

Asked by sudesh gupta

Hi,

I want to see variation of cross section with respect to polarization of incoming beam. In run_card, I found information that how to set polarization of incoming beams (beam1 and beam2) for one run. But I want to plot cross section with respect to polarization of incoming beam (say beam1) having range from -50 to + 50. What changes I need to do that in run_card.

Thanks

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Olivier Mattelaer
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Olivier Mattelaer suggests this article as an answer to your question:
FAQ #2186: “How to script MG5 run?”.

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sudesh gupta (sudesh12) said : 		#2

I have seen "FAQ#2186". I found that scan over parameters of param_card can be done by "set scan:[ ]". So, I have two questions,
1) We can set some specific value to polarization. If I want to scan over P, what I need to do?
2) I need to plot cross section with respect to polarization, but in run_card that option is not available like we can plot pt, mt, eta....etc.

May be answers of these questions are available in "FAQ#2186". Unfortunately I couldn't find.

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Best Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

1) No you can not use syntax like scan: for the run_card.
The only method is to use the FAQ in order to do a scan in a more manual way
launch
set polbeam1 -100
launch
set polbeam1 -50
launch
set polbeam1 0
launch
set polbeam1 50
launch
set polbeam1 100

then you can use the trick explained at the end of the first example of the FAQ:
launch MYDIRECTORY -i
       print_results --path=./cross_section_polbeam.txt --format=short
to have all the value of the cross-section in a single file.

With that file, it should be trivial to make a plot in function of the cross-section. However, we do not offer automatic tool for that.
If you want to create an extension of MG5aMC to automatically do such plot, I would be happy to merge it into the code.

Cheers,

Olivier

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sudesh gupta (sudesh12) said : 		#4

Thanks Olivier Mattelaer, that solved my question.