3 bodies decay

Asked by Dumitriu Ana on 2020-10-23

I am really new in madgraph.I have a naive question: how to enable 3 bodies decay?
I have in MG5_aMC_v2_6_6/Template/Common/Cards/madspin_card_default.dat:
# specify the decay for the final state particles
decay H++ > all all all
decay H-- > all all all
decay H+ > all all all
decay H- > all all all
Thank you for your help!

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Olivier Mattelaer (olivier-mattelaer) said :


MadSpin does not support three body decay (at least in the normal mode including off-shell effects and spin-correlation).
However for Higgs processes we typically do not care of both and in that case, you can simply let the parton-shower program to decay them (especially if you just want all of them).

MadSpin can also do it if you setup it with the special mode
set spinmode none
which stands for no off-shell effects and not spin-correlation between production and decay.

Additionaly, note that "all all all" is likely a very bad syntax if you have two body decay possible. Indeed if you have some two body decay, the all all all with contains "2 body decay plus photon or gluon" which will lead to divergencies.



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