MadGraph5_aMC@NLO

sytnax in decays

Asked by Tania Robens

Sorry I am sure this has been asked, but cant find the answer

The difference between

p p > A A, (A > B B)

and

p p > A A > B B B B

is that in the first, A's are on-shell (there are also more diagrams in the second, but currently I am concerned about onshellness...) ?

I get a large difference in cross sections (factor 2), and the main diagram is the same, so... ??

Thanks Best Tania

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

Hi,

p p > A A > B B B B

is the same as
p p > A > B B B B

Since the meaning of > A > is to have at least one "A" in s-channel.
Repeating the A multiple times does not ask for at least two "A" in s-channel.
So this explains the additional diagrams.

Otherwise, yes the first syntax is associated to an onshell cut (x times the width), where the value of x is an input in the run_card (bwcutoff). The default value is already quite large (15) and using much bigger number is not advised.

Finally, you also need to be carefull with cuts since default cut might not be the same with both syntax, (in particular check the valud of cut_decays that can prevent some cut to be applied in the first syntax)

Cheers,

Olivier

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Tania Robens (tania-robens) said : 		#2

Thanks Olivier Mattelaer, that solved my question.

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Tania Robens (tania-robens) said : 		#3

It was the cuts !! Thanks