Pythia not simulating ISR for non-SM final states

Asked by Jared Barron on 2019-05-21

I'm trying to use the HAHM_variableMW_v3_UFO model in Madgraph (version 2.6.5) to simulate the process g g > h, h > h2 h2, and then run events through Pythia 8 and Delphes. I'm expecting Pythia to shower ISR, and pass that on to Delphes. Instead, Pythia does nothing, and its output file is empty. If I force the h2 particles to decay to SM particles, e.g. muons, Pythia produces ISR as expected. This is for an LLP study, so in general I need to be able to run Pythia and Delphes for final state particles that do not decay, with the possibility that all final state particles are non-SM. Is there a way to do this? Thank you very much.

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You should get more accurate answer from Pythia8 author on this topic.
My two cent contribution here is that if you want to allow the h2 to decay within PY8, then you have to provide within the param_card what are the branching ration of the h2 to other particle. Without that information, PY8 will indeed fail.

One possibility is to ask MG5aMC to compute such branching ration by setting the associate width within the param_card to "auto"



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