MadGraph5_aMC@NLO

Method to generate polarised W bosons using DECAY package

Asked by Songshaptak De

Hello ,

I want to look into the decay products of the longitudinaly W-boson, generated from vector boson scattering process. Can you tell me the steps to do it using the DECAY package of the MADGRAPH or by any other means?

Regards,
Shaptak

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi Shaptak,

The DECAY package was part of MadGraph4.
It might have been distributed with some version of MadGraph5.
And was certainly dropped from the code when we released MG5aMC.
Consequently we do not provide any support on that package.

I know people still use it after that we dropped it.
For example here: https://twiki.cern.ch/twiki/bin/view/Main/MadgraphPolarization
But this seems to be quite old topic as well.

I do not have any solution to your problem right now. One think that you might want to check is the ability for HERWIG to do such decay. In principle they use the polarization matrix formalism for the decay, so if you can force it to be pure longitudinal in this case.
They might be able to handle correctly such decay.

This is actually a concept that I have never fully understood. It is weird to me to use an onshell concept for offshell particles.
Especially since this concept is not lorentz invariant. The good news for you is that I have recently move forward to implement something within MG5aMC (and then MadSpin) to be able to study those effects. This will allow me to quantify those problems.
If they are not important, then I will release that code and this should give a good way to preserve polarization information within the decay.

Cheers,

Olivier

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