Non-leptonic hadron decays: preferred paths?

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Discussion Overview

The discussion revolves around the interactions involved in non-leptonic hadron decays, specifically focusing on whether there is a preferred interaction for these processes and the implications of coupling constants and energy scales on these interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that hadron decays involving a change in quark flavor must occur through weak interaction, while decays without flavor change could occur through strong, weak, or electromagnetic interactions.
  • Another participant agrees that decays without flavor change can occur through multiple interactions and emphasizes that the strong interaction typically dominates due to its strength.
  • It is noted that the coupling constant of the strong force is dependent on energy and that the concept of "distance of quarks" is not meaningful in the context of hadrons.
  • One participant mentions that the weak interaction is generally negligible when strong or electromagnetic interactions are available, with rare exceptions like the J/Psi where strong interactions are suppressed enough to allow electromagnetic decays.
  • A later reply acknowledges the importance of the QCD scale, indicating that it is relevant for understanding hadron binding energies and the limitations of perturbation theory.

Areas of Agreement / Disagreement

Participants generally agree on the dominance of the strong interaction in hadron decays, but there is ongoing exploration regarding the conditions under which other interactions may play a role. The discussion remains unresolved regarding the preferred interaction and the implications of coupling constants.

Contextual Notes

Participants express uncertainty about the relationship between energy scales and coupling constants, as well as the implications of the QCD scale on hadron decays. The discussion reflects a need for deeper exploration of these concepts without reaching definitive conclusions.

terra
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My background of some introductory courses in particle physics has left me with severe shortcomings.

Say we start from a hadron, which decays purely to other hadrons. My question is this: through which interaction does the process take place? Is there a preferred interaction, and why/why not?
Let me put my thoughts/guesses/current understanding here.
A process in which the flavour of one or more quarks in the original hadron changes, must happen through weak interaction, and there are no other options.
Processes in which the flavours don't change could happen either through strong, weak or electromagnetic interaction. Right? Now, my guess is that there is a preference. How should I see this exactly? I thought about comparing the coupling constants, but I've understood that the coupling constant of the strong force depends on the distance of the quarks. Then again, how far can I get the quarks from each other depends on the energy they have. So once I fix the energy scale, I would be able to compare the couplings? Or is there an easier approach? Or am I missing something?
 
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terra said:
Processes in which the flavours don't change could happen either through strong, weak or electromagnetic interaction. Right?
Right.

terra said:
I thought about comparing the coupling constants, but I've understood that the coupling constant of the strong force depends on the distance of the quarks.
It depends on energy, but binding energies in hadrons are always at the QCD energy scale. "Distance of quarks" is not a meaningful concept in hadrons.
The strong interaction is so strong that it nearly always dominates.
The electromagnetic interaction is significantly weaker.
The weak interaction is negligible if one of the two other interactions is available.

Only in rare cases like the J/Psi the strong interactions gets suppressed enough to see electromagnetic decays.
 
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mfb said:
It depends on energy, but binding energies in hadrons are always at the QCD energy scale. "Distance of quarks" is not a meaningful concept in hadrons.
The strong interaction is so strong that it nearly always dominates.
The electromagnetic interaction is significantly weaker.
The weak interaction is negligible if one of the two other interactions is available.

Only in rare cases like the J/Psi the strong interactions gets suppressed enough to see electromagnetic decays.
I see, thank you for your insight. I take that by the qcd scale you mean the scale at which the coupling constant diverges, and as such perturbation theory can't be used.
 
Last edited:
There is a parameter called QCD scale, it is important for hadron binding energies.
 

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