Syntax for producing interference between tZ and WZ+b

Asked by Aaron Webb on 2021-01-25

Dear experts,

I'm trying to measure the interference between tZ and EWK WZ+b by simulating them separately, and then simultaneously, but I'm struggling to define a process that generates both tZ and WZ+b.

I use this line to generate tZ (along with the charges flipped):
generate p p > t b~ j Z $$ W+ W- , (t > w+ b , w+ > l+ vl) , Z > l+ l- QED=6

and this to generate WZ+b:
generate p p > w+ Z b b~ j $$ t t~, w+ > l+ vl, Z > l+ l- QED=6

I assumed this should produce both, but no diagrams with tops are generated:
generate p p > w+ b b~ j Z, w+ > l+ vl, Z > l+ l- QED<=6

I've also tried a more general command, but I get the same issue:
generate p p > l+ l- l+ vl b b~ j QED=6

Is there something wrong with my syntax that explains why madgraph isn't generating any tZ for those last two lines?

Thanks in advance for your help!

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Robert Crook (robertcrook) said : #4

I am having a same problem.


You are likely looking for the following syntax:
 generate p p > w+ b b~ j Z QED<=4 , w+ > l+ vl, Z > l+ l-

The coupling restriction are per block and not for the full process



Aaron Webb (afwebb) said : #6

Hi Olivier,

Thanks for the response. Strangely when I use that syntax I now generate only tZ diagrams, so only QED=4. Is there something else I need to adjust to tell madgraph to generate both QED=4 and QED=2 diagrams?


The syntax QED<=4 works fine for me and I have both QED=2 and QED=4 Feynman Diagram displayed for the above syntax


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