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Homework Help: Particle Interaction Question

  1. Nov 29, 2011 #1
    1. The problem statement, all variables and given/known data

    Which of the following reactions are forbidden and why?

    [itex]\pi^{0}\rightarrow\gamma[/itex]


    2. Relevant equations

    None?

    3. The attempt at a solution

    I'm pretty sure that the decay doesn't occur (it's forbidden) but I don't know why. I know that it decays most of the time into two gammas.

    I think the problem is that I don't understand what characteristics [itex]\gamma[/itex] (photon) has. As in, when I do other problems like this I look at the quark content and the flavors, compare Strangeness and Lepton numbers etc etc.

    Thanks!
     
  2. jcsd
  3. Nov 30, 2011 #2

    fzero

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    You need to consider conservation of the spin quantum number.
     
  4. Nov 30, 2011 #3
    So if the pion has s=0 but gamma has s=1, why does the pion decay to two gammas but not to one?
     
  5. Nov 30, 2011 #4

    fzero

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    What are the allowed values of total spin for a two photon system?
     
  6. Nov 30, 2011 #5
    Okay I looked it up, and found that they combine so that the spin projection cancels and are spin-0.

    Sorry I had to ask some menial stuff from you, my book doesn't spend any time going into detail about these things. There was no mention of the photons :[

    Thanks for the help.
     
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