Neutron Decay: Questions & Answers

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Discussion Overview

The discussion revolves around neutron decay, specifically the factors influencing decay probabilities and the role of quark masses and the CKM matrix. Participants explore theoretical scenarios regarding quark types and decay processes, including hadronic and leptonic decays.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions what prevents neutron decay into udc or udt beyond mass/energy considerations.
  • Another participant clarifies that a neutron is composed of udd and finds the initial question confusing.
  • It is proposed that if heavier quarks were much lighter, they would not be considered different particle types, but the CKM matrix influences decay probabilities, suggesting that d->u has a higher amplitude than d->c or d->t.
  • Discussion includes the W boson's decay into quark-antiquark pairs, noting that energy conservation prevents it from decaying into a single meson.
  • A participant reflects on their earlier misunderstanding regarding decay probabilities and acknowledges the role of the CKM matrix.
  • Questions arise about the suppression of leptonic decay in the case of the Λ^0 baryon compared to neutron decay, with participants expressing uncertainty about the differences in branching ratios and phase space factors.

Areas of Agreement / Disagreement

Participants express differing views on the implications of quark masses and decay probabilities, particularly regarding the CKM matrix's role. The discussion remains unresolved regarding the specific factors influencing decay rates in various scenarios.

Contextual Notes

Limitations include assumptions about quark masses and the implications of the CKM matrix, as well as the dependence on energy conservation in decay processes. The discussion does not resolve the complexities of branching ratios between leptonic and hadronic decays.

Dalor
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Hi, I have questions on the neutron decay

What prevent the neutron to decay in udc or udt except mass/energy consideration ?

If we do the assumption that (udc) and (udt) have the same mass than the proton (yes I know, this doesn't make sense) the three decay (p, udc, udt) woulld have the same probability ?

Also this is only energy consideration that prevent the ##W## to decay in ##q \bar q## too?

Thank you
 
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A neutron is udd. Your question is confusing.
 
If the heavier quarks would be much lighter we would see them in everyday life, too.

As extreme case: If they would have the same mass we wouldn't consider them as different particle types.
Dalor said:
If we do the assumption that (udc) and (udt) have the same mass than the proton (yes I know, this doesn't make sense) the three decay (p, udc, udt) woulld have the same probability ?
No, there is still the CKM matrix. d->u has a higher amplitude than d->c or d->t.
 
Dalor said:
Also this is only energy consideration that prevent the WWW to decay in q¯qqq¯q \bar q too?
The W does decay to ##q\bar q##. However, the final state cannot be a single meson due to energy conservation and the quarks therefore quickly hadronize. Most of the time W decays hadronically.
 
Oh I was definitely not paying attention !

mfb said:
No, there is still the CKM matrix. d->u has a higher amplitude than d->c or d->t.

Of course my mistake.
(Yes, they would be same particle, it was only for the "thought experiment".)

Orodruin said:
The W does decay to ##q\bar q##. However, the final state cannot be a single meson due to energy conservation and the quarks therefore quickly hadronize. Most of the time W decays hadronically.
Yep I meant the hadronic decay ##u \bar d##, ##u \bar s## and so on.

My question came from the ## \Lambda^0##, the leptonic decay is suppressed by several order of magnitude. I don't understand why since BR between leptonique and hadronic decay is not so low and it seems a big difference considering only phase space factor, no ? And the other hand in neutron decay there is only the leptonic decay, that was why I ask the kind of meaningless question about "the neutron decay if quark add same mass".

Thank you.
 

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