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How is the Higgs decay into Z and gamma modeled in POWHEG?

In my PhD work on Higgs phenomenology, I'm using POWHEG+PYTHIA to generate events for the H → Zγ channel, which is a crucial probe for new physics. The documentation is quite technical. I need a clearer picture of how the matrix elements and radiation are handled specifically for this loop-induced process to validate my analysis chain and estimate systematic uncertainties properly.

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By Suresh Answered 9 months ago

This is an excellent and essential question for anyone doing precision work with this channel. I've worked with these simulations for BSM searches. In POWHEG, H → Zγ is treated as a loop-induced process from the start. This means the core matrix element already includes the dominant contributions from heavy particles like top quarks and W bosons circulating in the loop. POWHEG's key role is to then generate the first, hardest QCD emission (radiation) from the initial quarks and gluons in a theoretically sound way, preserving the NLO accuracy of the inclusive cross-section. After that, it hands the event off to PYTHIA for parton showering. For your systematics, focus on the scale choices for that initial radiation and the loop couplings.

   

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