MadGraph5_aMC@NLO

Recreating diagrams from lhe event

Asked by rchan

I have a LHE file for the process p p > j j g

the gluon is radiated by either by initial state quarks or final state jets.

Now is there any way I can identify them in each event? or maybe reconstruct the diagram from LHE file?

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

Such information are not present in the LHE file.
Actually, we do not have a way to compute such information at all.
The first reason is that such information is not gauge invariant and lead to breaking lorentz invariance in our framework.

In our setup, we do compute the QCD part of the computation by projecting each diagram on a color basis (we use the fundamental basis). A given diagram can be decompose onto various element of the basis.
Since the squaring of the amplitude is done based on the color matrix computed for the basis, we do not have the information of the amplitude square of a given diagram, so even if we were assuming that we could neglect all interference and agree to fix the gauge in one specific way, we would not be able to compute such type of number.

Cheers,

Olivier

And in a way, this can not be defined in a correct way since such statement will not be gauge invariant.

The main reason is that such information are not needed for Parton-Shower, and obviously this is also related that such statement are not

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