MadGraph5_aMC@NLO

processes generation in madweight 4

Asked by Tim Lu

Hello,
When I want to use madweight 4 to do the matrix element method for WW scattering process :
I separately generated two kinds of processes :
(one let w to decay, but the other not.)

u d > d W+ W- u @1 # First Process
QCD=0 # Max QCD couplings
QED=99 # Max QED couplings

u d > d W+ W- u > d e+ ve~ e- ve u @1 # First Process
QCD=0 # Max QCD couplings
QED=99 # Max QED couplings

But the generating Feynman diagrams for the second process are very strange, it just has very little diagrams, I don't know what is the problem ?
Why the second process not just like the first one, but let w to decay ?

Thanks a lot ! !

Best,
Tim

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

Hi Tim,

u d > d W+ W- u > d e+ ve~ e- ve u @1 # First Process
QCD=0 # Max QCD couplings
QED=99 # Max QED couplings

This is not the way to generate the daigram. The particles named in > > are request to appear somewhere in s-channel.
Which can provide some really un-expected diagram.

The correct syntax in your case is the decay chain syntax:
u d > d (W+ > e+ ve) (W- > e- ve~) u @1 # First Process
QCD=0 # Max QCD couplings
QED=99 # Max QED couplings

Note as well that
1) MW4 can only compute weight for process in decay chain syntax
2) We are going to release MW5 as the official release of MadWeight in principle next week.
This MW5 version is already used by both CMS and ATLAS in various lab. So I would strongly advise to start to use that version.

Cheers,

Olivier

Revision history for this message
Tim Lu (timluyu) said : 		#2

Thanks Olivier Mattelaer, that solved my question.