MadGraph5_aMC@NLO

NP settings in MadGraph

Asked by Sihyun Jeon

Hi Olivier,

I have a question about the "NP settings" in MadGraph.

After looking at the slides in [1] Exercise IV: Interference part.

I've tested

import model bbll_UFO # model is in FeynRules
a. generate p p > e+ e-
b. generate p p > e+ e- NP^2==0 # assumed this would be same as the SM term

I found that a. and b. both contains only the SM Feynman diagrams that does not have any NP vertices.
But the results (cross sections) were significantly different so I wonder if NP^2==0 is a syntax that should not be used no matter what (== does this not make sense at all?).

import model bbll_UFO
generate p p > mu+ mu- #NP^2==0 # for a. removed NP^2==0, for b. kept NP^2==0
output NPeqeq0
launch
set cmubbll 0.01
set nevents 3000
set use_syst False

Regards,
Sihyun.

[1] https://indico.cern.ch/event/796134/contributions/3560246/attachments/1908914/3157345/19_09_19_tuto_Vietnam.pdf

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

Hi,

The reason is likely to be related to scale uncertainty, the default run_card is likely not the same for the two syntax since it assumes that you are in interference mode in one case and not in the other.

So your default scale is not the same (and maybe also other parameter). If you use the same run_card for both computation you should get a good agreement.

Cheers,

Olivier

> On 26 Jul 2021, at 14:15, Sihyun Jeon <email address hidden> wrote:
>
> generate p p > e+ e-

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Sihyun Jeon (shjeon) said : 		#2
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Sihyun Jeon (shjeon) said : 		#3

Thanks Olivier Mattelaer, that solved my question.