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Neutral pion decay

  1. May 15, 2009 #1
    So I know the neutral pion decays as
    [tex] \pi \rightarrow \gamma\gamma [/tex]

    my question is though, what forbids this from being an electromagnetic decay? I know it is not decaying via the strong force as there are no quarks resulting from decay. However, I do not see what forbids this from decaying via the EM force, if it is spitting out two gammas, which is the EM force carrier. Parity, G-parity, and Energy are conserved, as well as strangeness and angular momentum, so, what exactly forbids this from being EM?
  2. jcsd
  3. May 15, 2009 #2
    What makes you think it isn't an electromagnetic decay?

    I would say that it is.
  4. May 15, 2009 #3


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    Gold Member

    EM it is, but anomaly.
  5. May 16, 2009 #4

    Hans de Vries

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    Science Advisor

    It's not forbidden but it would be under conservation of
    the axial current density [itex]j_A^\mu[/itex]. (The latter is only conserved
    together with the Chern Simons current of the EM field)

    Regards, Hans
    Last edited: May 16, 2009
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