MadGraph5_aMC@NLO

generate four jet events with all the possible diagrams

Asked by amir subba

Hi all,
I am trying to generate four jet events in electron-positron collider. The syntax i am using is:
e- e+ > j j j j
What I wanted is all the possible diagrams like:
e- e+ > w- w+, w- > j j, w+ > j j
e- e+ > z z, z > j j, z > j j
e- e+ > h z, h > j j , z > j j
e- e+ > a a, a > j j, a > j j
e- e+ > a z, a > j j, z > j j
e- e+ > j j j j, without intemediate weak bosons.
Could anyone suggest me how to proceed to generate all these diagrams in one go. Also, i tried to generate 4j events with intermediate photons but the number of events returning are very few. Could anyone clarify on this too.

Thanks!!

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

You need to use
generate e+ e- > 4j QED<=99

The QED<=99 removes the automatic assignment of QCD/QED restriction which is design to throw away QED contribution when QCD contribution does exists.

Cheers,

Olivier

OS: e- e+ > a a, a > j j, a > j j syntax does not make sense since the "," is associated to a Narrow Width Approximation which is obviously not valid for massless particle

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amir subba (amir4hep) said : 		#2

Thanks for the quick reply Olivier.
Actually I wanted to keep four jet events with intermediate photons as one of the background to WW signal. So, in this line can you suggest me a way out to present how to generate events with say off-shell photons.

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Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi,

One need to be carefull about what you want here:
1. if you really want only photon, you are breaking gauge invariance and therefore any gauge choice fixing will lead to a different result. One consequence is that the result will not be lorentz invariant (since our gauge fixing choice depends on the frame)

2. A correlated point, is that obviously asking for only photon will neglect the interference term with the other diagram and therefore you either have to include that interference in top (in this case I doubt that you can simply neglect it )

So my suggestion would not to request a particle but to forbid some particle to be onshell.
you can use the syntax
generate e+ e- > 4j $ Z w+ w- h QCD=0

Where the $ syntax forbids the Z w+ w- h to be onshell but does keep the diagram to preserve gauge invariance within the off-shell region.

Cheers,

Olivier

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