Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

\eta\to\pi^0\gamma decay (Why this decay is forbidden by J?)

  1. Apr 20, 2015 #1
    Decay \eta\to\pi^0\gamma is forbidden by C parity. But why this decay is also forbidden by statistics (J)?

    pi^0 spin is 0
    photon spin is 1

    But there are can be different situations with full orbital angular momentum of pi^0\gamma.
    J=L+S and must be 0. Look like L is 0. But why? Why we can't have L=1 in this case? (unlike in \rho\to\pi^0\gamma decay)
    Last edited: Apr 20, 2015
  2. jcsd
  3. Apr 20, 2015 #2


    User Avatar
    Gold Member

    I would say that your first has spin 0, while the product has a spin 0 particle and a photon which is a spin 1 particle.
  4. Apr 20, 2015 #3


    User Avatar
    Gold Member

    If you put it in a J=1 state the total wavefunction is antisymmetric, and it has to be symmetric because of Bose statistics. [quoting from Vanadium 50 in the ref. link]

    rho is a J=1 particle. It can't decay though to pi0 pi0. A similar question has be asked/answered here:
  5. Apr 20, 2015 #4


    User Avatar
    Gold Member

    Again I am saying that the rho has J=1, so angular momentum conservation does not prohibit it to decay in a J=1 + J=0 particle.
    The eta has J=0. And you try to make it decay into a J=1 and a J=0 particle? you can't compare these.
    It's not only the CG coefficients, keep reading the conversation.

    If you try to make the last configuration of pi0 and gamma to have a total angular momentum 0, then you have to set the orbital angular momentum of the two products to be L=1.
    But then you are having an antisymmetric wavefunction describing your boson final states
  6. Apr 20, 2015 #5

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    I think this is much easier to see semiclassically: you are asking if a 0- --> 0- + radiation state is possible. It is not. A 0- state can have only monopole moments, and there are no magnetic monopoles, and the electric monopole is simply charge: zero in this case. Since no moment changes, there can be no radiation.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook