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Weak interaction - half-lifetime of a decay

  1. Jan 28, 2007 #1
    I need help with an exercise about the weak interaction:

    How do the mass, the q-value and the vertices depend on the half-lifetime of a decay?

    The myon decay has a half-lifetime of 0.0000015 seconds, the neutron decay has a half-lifetime of 607 seconds.

    Why is there such a big difference between this two times? Is this because the q-value of a myon is 105MeV while the q-value of a neutron is 0.782MeV? Or has it maybe to do with the involved mas?

    Please help me!!!
  2. jcsd
  3. Jan 30, 2007 #2


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    Really good exersice. Muon decay is covered in most textbooks, and all the other weak decays except the neutron scale with the quintic power of the mass, in a first approximation. For the neutron, which has a rare decay between two quarks of similar masses in the presence of another one of the same order, the calculation is troublesome and I only know of a textbook covering it, probably Griffith's.

    You can argue that the q-value is not the whole history if you consider the decay of the charged pion to muon.
    Last edited: Jan 30, 2007
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