Generating W' events with SM interference

Asked by Agostino on 2021-02-01

Dear MG5 team,
I am trying to generate W' events in s-channel with the SM interference.
I am using the model WEff_UFO
At the beginning I was trying in the following way :
generate p p > wp+ > t b~
add process p p > wp- > t~ b
add process p p > t~ b
add process p p > t~ b
but this does not include the interference even if there is a ~5% difference in the cross section of LH and RH processes.
I then try this other way:
generate p p > t~ b NP^2>0
add process p p > t~ b NP^2>0
This time the interference is correctly there but I am not able to use MadSpin for the top decay.
I also tried to do the following:
generate p p > t b~, (t > w+ b, w+ > all all) NP^2>0
add process p p > t~ b, (t~ > w- b~, w- > all all) NP^2>0
but in this case no BSM process is generated.
Am I doing something wrong or ignoring something?
Your help will be very much appreciated.
Best,
Agostino

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2021-02-03
Last query:
2021-02-03
Last reply:
2021-02-01

Hi,

Your first syntax is certainly weird and is likely not that meaningful.
Your second syntax is fine, but you obviously forbid the SM contribution.
But indeed the syntax using "^2" have some limitations, namely that you can use the decay chain syntax (namely the one with ",")
which therefore forbids madspin, since madspin rely on the generation of matrix-element with the decay chain syntax to make the decay.

I'm not 100% sure to know what you are looking for, but maybe you can try
generate p p > t~ b NP<=99
output
launch
MadSpin=ON

or maybe
generate p p > t~ b NP==1
output
launch
MadSpin=ON

Cheers,

Olivier

Agostino (agomag) said : #2

Dear Olivier,
thanks for your fast replies. I wanted to produce the process pp to tb via both the SM W boson and the BSM W' boson taking into account he interference too. The first solution you proposed seems to work fine.

Cheers,
Agostino

Agostino (agomag) said : #3

Thanks Olivier Mattelaer, that solved my question.