W Boson and different generations of quarks

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    Boson Quarks W boson
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Discussion Overview

The discussion centers on the interactions of W bosons with quarks, specifically whether a W boson can convert an up quark into a down quark within the same generation. Participants explore the implications of quark generations and the role of the CKM matrix in these transitions, as well as the conditions necessary for such processes to occur.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that up and down quarks belong to the same generation, while others clarify that they are categorized as up-type and down-type quarks, respectively.
  • It is proposed that the W boson can couple to up and down quarks, with the coupling to down quarks being the strongest, but transitions to strange and bottom quarks are also possible.
  • One participant references the CKM matrix, suggesting that while transitions between up and down-type quarks are theoretically possible, they are not equally favored, with some transitions being rare.
  • Another participant emphasizes that for a transition to occur, additional conditions such as energy and momentum conservation must be satisfied, noting that certain decays, like W → tb, are impossible.

Areas of Agreement / Disagreement

Participants generally agree that W bosons can facilitate transitions between quarks of the same generation, but there is no consensus on the likelihood of specific transitions or the implications of energy conservation on these processes.

Contextual Notes

Some discussions involve the CKM matrix and its role in determining the probabilities of quark transitions, but the exact implications and the conditions under which transitions can occur remain unresolved.

Richard McCarthy
Can a W Boson convert an up quark into a down quark of the same generation? Where can I find a resource to understand what all the possibilities are for an up quark converting into other quarks of same or other generations?
 
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The first generation of quarks is "up-quarks and down-quarks" by definition, up and down are always in the same generation. The second generation is charm and strange and the third one is top and bottom.
Richard McCarthy said:
Where can I find a resource to understand what all the possibilities are for an up quark converting into other quarks of same or other generations?
Coupling to the W is the only option, and while the coupling with an up-quark to a down is the strongest one, coupling to strange and bottom is also possible.
If the W is not real (e.g. in a beta decay), conservation of energy can make some processes impossible.
 
By looking at the CKM matrix you can immediately see that the transitions between up and down-type quarks are all possible in principle (yet not equally favored)...So for example you could see the transition t \rightarrow b, but you would rarely see t \rightarrow s... yet again you could see a c \rightarrow s but it's also possible (not extremely rare) to see c \rightarrow d. In general I think the CKM matrix tells you that transitions are more likely to occur within the same generation rather than the other...
The transitions happen via the W bosons (or charged currents), since there are no flavor changing neutral currents observed.
 
Richard McCarthy said:
Can a W Boson convert an up quark into a down quark of the same generation?

I understand that by up and down quark you mean up type quark (t,c,u) and down type quark ( b,s,d). The answer is yes.
Richard McCarthy said:
Where can I find a resource to understand what all the possibilities are for an up quark converting into other quarks of same or other generations?

The couplings of the W boson to any up type down type quark pair are described by the CKM matrix ( see http://pdg.lbl.gov/2014/reviews/rpp2014-rev-ckm-matrix.pdf for their measured values).

As mfb mentioned, for a process to be possible other conditions have to be met as well, such as Energy and Momentum conservation.

So, for example, the decay W\rightarrow tb is impossible.
 
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