Quark mixing factor in CKM matrix

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Discussion Overview

The discussion revolves around the quark mixing factors in the CKM matrix, specifically the coupling constants such as ##V_{ub}## and ##V_{us}##. Participants explore the implications of these factors in the context of weak interactions and their relationships to quark and anti-quark transitions, as well as specific decay processes like that of the charged Kaon.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the quark mixing factor ##V_{ub}## is the same for various transitions involving quarks and anti-quarks, questioning if this is due to the weak interaction's inability to distinguish between them.
  • Another participant asserts that there is no known interaction that converts a quark into an anti-quark, as this would violate baryon number conservation.
  • A participant explains that the equality in magnitude of the couplings between ##u## and ##b## and between ##\bar{u}## and ##\bar{b}## arises from the Hermitian nature of the Lagrangian density.
  • One participant references the decay of the charged Kaon, noting that the hadronic part of the current has coupling ##V_{c\bar{s}}##, which they claim is the same as ##V_{cs}##.
  • Another participant clarifies that the process is not a direct transition between quarks and emphasizes the need for the coupling ##V_{us## in the context of the decay diagram.

Areas of Agreement / Disagreement

Participants express differing views on the implications of quark mixing factors and their relationships to specific decay processes. There is no consensus on the interpretations of these couplings and their physical significance.

Contextual Notes

Some statements rely on assumptions about the properties of the Lagrangian and the nature of weak interactions, which may not be universally accepted or fully resolved within the discussion.

Amith2006
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I find that the quark mixing factor say for example ##V_{ub}## is the same for:
u ##\Leftrightarrow## b
##u\Leftrightarrow\bar{b}##
##\bar{u}\Leftrightarrow## b
##\bar{u}\Leftrightarrow\bar{b}##
Does this have something to do with weak interaction being unable to distinguish these from one another?
Thanks in advance.
 
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There is no (known) interaction which turns a quark into an anti-quark as that would violate baryon number.

For the coupling between ##u## and ##b## being equal (in magnitude) to the coupling between ##\bar u## and ##\bar b##, this is a simple consequence of the Lagrangian density being Hermitian.
 
Orodruin said:
There is no (known) interaction which turns a quark into an anti-quark as that would violate baryon number.

For the coupling between ##u## and ##b## being equal (in magnitude) to the coupling between ##\bar u## and ##\bar b##, this is a simple consequence of the Lagrangian density being Hermitian.
I can understand that the coupling between u and b is equal (in magnitude) to the coupling between ##\bar{u}## and ##\bar{b}## due to the Hermitian property but in the decay of charged Kaon,
##K^+ \rightarrow \mu^+ + \nu_\mu##
the hadronic part of the current has ##V_{c\bar{s}}## which is the same coupling as ##V_{cs}##.
 
Last edited:
It is not a transition between them, that is the point.
You can rotate the diagram to get u -> s+W+, for example (no c involved in a kaon decay). The vertex stays the same, so you need Vus.
 
Sorry ##V_{us}##. Ah, now I get it. Thanks.
 

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