MadGraph5_aMC@NLO

cut_decays! Cut decay products

Asked by Ribella

Hi,

I want to calculate the process e- e+-->w+, w-, gam in the Standard Model (gam is the photon). Here, w+ and w- bosons decay w+ > jj and w- > l vl.
We use the following cuts in the run card;

ptj=20 GeV
Ptvl=15 GeV
Ptl=20 GeV
Ptgam=50 GeV
etaj=5
etal=2.5
eta gam=2.5.

The question I want to ask is this. When I do False=cut_decays! Cut decay products the code on the cuts, the results are different when True=cut_decays! Cut decay products with the cross section. Which do you think is correct?

Best Regards,

Ribella

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Conceptually both are correct, it is just that this is two different computation.
The reason for cut_decays=False is that often you do not want to cut lepton/jet coming from onshell decay such that you simply have the narrow width approximation for the cross-section. If you want to have cuts then you have to set cut_decays=True.

For your question, since you specify cuts like "ptl" it sounds clear that you want to have cut_decays=True.

Cheers,

Olivier

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Ribella (ribella) said : 		#2

Thanks Olivier, that solved my question.