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Decay into an electron and an electron-anti-neutrino?

  1. Mar 8, 2007 #1
    [tex] \pi ^- \rightarrow \mu^- +\bar{\nu_\mu} [/tex]

    Why doesn't it decay into an electron and an electron-anti-neutrino? I guess it has something to do with the conservation of the helicity. But how does it work?
  2. jcsd
  3. Mar 8, 2007 #2

    Meir Achuz

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    The pi-->e nu decay occurs but at about 10^-4 compared to the mu decay channel. Helicity is involved. Because the pi has spin zero, the two decay particles have to have the same helicity (giving total S_z=0). But the V-A theory of weak interactions tries to give them opposite helicities. This mismatch leads to a factor (m_e/m_mu)^2 in the ratio of e to mu decay.
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