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I W Boson and different generations of quarks

  1. Aug 8, 2017 #1
    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?
  2. jcsd
  3. Aug 8, 2017 #2


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    Staff: Mentor

    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.
    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.
  4. Aug 8, 2017 #3


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    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 [itex]t \rightarrow b[/itex], but you would rarely see [itex]t \rightarrow s[/itex]... yet again you could see a [itex]c \rightarrow s[/itex] but it's also possible (not extremely rare) to see [itex]c \rightarrow d[/itex]. 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.
  5. Aug 9, 2017 #4
    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.

    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 [itex]W\rightarrow tb[/itex] is impossible.
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