VBF double Higgs production process

Asked by Brunella D'Anzi on 2021-05-13

Dear Madgraph Experts,

I would need help in order to understand what are the processes that I exclude if I generate MC events using the following command

generate p p > h h j j $$ z w+ w- / a j QED=4

instead of

generate p p > h h j j $$ z w+ w- .

This would be the first step for me for simulating signal events of non-resonant double Higgs Boson pair production produced via VBF mechanism with final state 4 charged leptons and b bbar. Is it meaningful to add " / a j" for this process and using the default setting QCD=0?

Thanks in advance,
Brunella

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Olivier Mattelaer (olivier-mattelaer) said :
#1

You do not forbids process but matrix-element.
If the set of matrix-element that you select like that are not gauge invariant then your computation will be meaningless.

If you use QED=4, you will see a warning that such syntax does not really exists and that your command will be interpreted as
QED<=4 so you will have both QCD and pure EW production.

If you do not precise those type of information (like in your second syntax) MG5aMC only includes the QCD production.

The "/ a j" means that you forbid any Feynman diagram with a photon, a gluon or a quark in your feynman diagram which can often leads to gauge invariance issue (and lorentz invariance issue). I do not know if in your case this is a gauge invariant sub-set.

You can use the command
check p p > h h j j $$ z w+ w- / a j QED=4
to have madgraph to apply some minimal check on lorentz invariance/ gauge invariance /...

Cheers,

Olivier

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