Questions about radiative decay modes

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Discussion Overview

The discussion revolves around the radiative decay modes of the K+ meson, specifically the decay process K+ -> pi+, pi0, gamma. Participants explore the mechanisms of inner bremsstrahlung (IB) and direct emission (DE), raising questions about the nature of radiation and the roles of particles involved in these processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the pi+ is responsible for radiation in inner bremsstrahlung and asks what causes its deceleration.
  • Another participant argues against the use of "deceleration" in this context, stating that inner bremsstrahlung is a radiative QED effect and that direct emission occurs before the pions are fully formed.
  • A subsequent post seeks clarification on whether direct emission photons originate solely from virtual particles and how to experimentally differentiate between direct emission and inner bremsstrahlung.
  • Another participant asserts that inner bremsstrahlung is the dominant mechanism, while direct emission is a minor correction, noting that the calculation of IB width is straightforward with QED, whereas DE involves more complex processes not fully explained by virtual particles and perturbative QCD.

Areas of Agreement / Disagreement

Participants express differing views on the nature of radiation in the decay processes, particularly regarding the roles of inner bremsstrahlung and direct emission. There is no consensus on the specifics of how these mechanisms operate or how they can be experimentally distinguished.

Contextual Notes

The discussion highlights limitations in understanding the mechanisms involved in the decay processes, particularly regarding the definitions and assumptions related to radiation and particle formation. The complexity of direct emission processes is noted, but not fully resolved.

jossives
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Let's take for example the decay K+ -> pi+,pi0,gamma

This can proceed via direct emission or inner bremsstrahlung. I have questions for each of these modes

1. For inner bremsstrahlung, it is a final charged product that radiates, correct? In this case the pi+. What is causing the deceleration of the pi+ such that it radiates?

2. Does direct emission only come from from virtual particles or can it come from (in this example) one of the 4 quarks in the final state?

Thanks for any help in advance
 
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I don't think it's appropriate to talk about "deceleration" in this context. IB is simply a radiative QED effect.

By definition, DE occurs before pions are fully formed. Fully formed pi0 is neutral and can't radiate, gammas emitted from fully formed pi+ are part of IB.
 
So the DE photons come only from the virtual particles and IB from the fully formed ones? How do you differentiate between these two modes experimentally?
 
IB is the dominant mechanism and DE is a tiny correction to that. IB width is easily calculated using QED, DE is much more nontrivial because you can't fully explain processes that go on during the decay of K in terms of virtual particles and perturbative QCD. I'm not an expert, but I'd imagine that spectra would be different.

See this presentation, hope it helps

http://www.lnf.infn.it/wg/vus/workshop07/Talks/Raggi.ppt
 

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