Pi 0 Decay: Chances of e+ e- Gamma vs e+ e-

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SUMMARY

The discussion centers on the decay of the pi zero meson (π0) into electron-positron pairs (e+ e-) and gamma photons (γ). It is established that the decay into e+ e- γ is favored over e+ e- due to the suppression of the latter by helicity constraints and conservation of angular momentum. The leading order contribution for the e+ e- decay, involving a single photon exchange, evaluates to zero, necessitating an intermediate state for the decay to occur. Understanding these mechanisms requires knowledge of quantum field theory and the role of electromagnetic coupling.

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  • Familiarity with electromagnetic interactions (alphaEM)
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Manel
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Hello everyone,
I found in the PDG booklet that pi 0 decay into e+ e- gamma is more likely to happen than to e+ e- only ..is there a reason that favorises the first decay?
 
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The decay to a single electron-positron pair is suppressed because what would be the leading order contribution, the diagram with the exchange of one single photon, evaluates to zero.
 
Orodruin said:
the diagram with the exchange of one single photon, evaluates to zero.
I didn't understand what you mean here. Would you please clarify. Thanks a lot
 
The decays must happen via an intermediate state. The intermediate state which would be contributing the most to the electron-positron decay based on the couplings is not allowed.
 
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Any resource detailing that ? So grateful
 
Complete understanding of this would require an introductory course in quantum field theory, usually given at universities somewhere in year 3-4.
 
Thanks a lot
 
also helicity suppression probably plays a role. a pseudoscalar decaying to to leptons will be suppressed by the mass of the lepton, due to conservation of angular momentum requiring a spin flip on one lepton. adding the photon will allow the lepton to not have to flip, thus trading the mass suppression for alphaEM.
 

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