MadGraph5_aMC@NLO

Confusion over the correct syntax to generate process

Asked by Saumyen Kundu

Hi,
Excuse me for this trivial (and potentially silly question).
I am bit confused while generating the process " p p -> w w j ". I tried 2 syntaxes.
1. generate p p > w+ w- j, (w+ > l+ vl), (w- > j j) @1
    add process p p > w+ w- j, (w- > l- vl~), (w+ > j j) @2
This gives: 2 processes with 176 diagrams

2. define ww = w+ w-; define l = l+ l-; define vll = vl vl~
    generate p p > ww ww j, (ww > l vll), (ww > j j)
This gives: 1 processes with 92 diagrams

I just wanted to know which one would be correct to use? Using the 2nd syntax, would I miss out on contributing diagrams or syntax-1 double counts some diagrams.

Thanks a lot for any help in advance.

With regards,
Saumyen

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

One think for sure is that syntax 2 is not the same as syntax 1.
They are not double counting in both cases but the decay allowed for the w is not the same with both syntax.

I would have expect that for your syntax2 you would get 4 decay channel
w+ > j j, w- > j j
w+ > l+ v, w- > l- v
w+ > j j , w- > l- v
w+ > l+ v, w-> l- v

But looks like the code does not behave as I would have expected and you actually only get one (according to HTML/info.html)
w+ > l+ v, w- > j j
handling correctly multiple definition of multi-particle with decay chain is complicated so this is likely why it does not detect correctly that you define multiple decay for all those particles.

In any case, I guess that you do not want the four decay (they are simpler syntax for that, like generate p p > ww ww j, ww > all all.
So your first syntax is likely the one that you want to use.

Cheers,

Olivier

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Saumyen Kundu (saumyen.k) said : 		#2

Thanks a lot, Olivier, for the clarification.

Basically, what I want is pp> ww+jets, where one of the w-bosons decays leptonically and the other one hadronically. I don't want both the w's to decay leptonically/hadronically.

So, I suppose the first syntax is what I should use, as you suggested.

Thanks a lot again.

Regards,
Saumyen

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Olivier Mattelaer (olivier-mattelaer) said : 		#3

Yes indeed,

Cheers,

Olivier