MadGraph5_aMC@NLO

Cuts on pt for 4-momenta sum of two particles

Asked by Dmitriy Zubov

Hi,
I want to limit PT for 4-momenta sum of two electrons in generation p p > z > e+ e-. Is it possible?
I tried this one, {0.0 = ptllmin ! Minimum pt for 4-momenta sum of leptons(l and vl)}
but faced the error : Survey return zero cross section. ( I think it's because there are no neutrinos).
Cheers,
Dmitriy

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

Hi,

 Since your cut are done at parton level BEFORE any showering/hadronization/detector level. Putting ANY cut on the ptll is indeed impossible. You are asking a two to one process and then having the Z to decay to two lepton.
Since madgraph uses collinear approximation for the beam (that's the typical PDF approximation ) then the quark comming from the proton are assumed to be without any transverse momenta. Therefore by conservation of momenta, the Z itself has 0 momenta.
Therefore asking a cut on the pt of the Z will throw away 100% of your cross-sections.

If you want such cut at parton level, you might want to look at p p > z j , z > e+ e- process instead

Cheers,

Olivier

PS: The syntax that you are using is breaking gauge invariance and returns unphysical results basically everywhere but onshell
This is actually the example that I use in my tutorial to try to discourage people to use this > X > syntax.
So please check for example this tutorial (not one of mine but this is the first I found online):
https://indico.ihep.ac.cn/event/7822/contribution/19/material/slides/0.pdf

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Dmitriy Zubov (zubov-dmitriy) said : 		#2

Thanks Olivier Mattelaer, that solved my question.