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Feynman diagram of secondary Sigma plus decay

  1. Oct 5, 2011 #1
    Can someone describe the Feynman diagram for the Sigma plus decay to a positive pion and a neutron? I'm fine with the primary decay to the neutral pion and a proton. There appears to be insufficient down quarks created.
     
  2. jcsd
  3. Oct 6, 2011 #2

    Hepth

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    uus > ud~ u d d

    Well one d d~ set can be made with a photon/gluon, while the s-> d can be a loop-level FCNC.

    OR

    uus : s---u
    uus : u---d
    via a W exchange, and the d dbar pair is made with a photon/gluon emission.
     
  4. Oct 6, 2011 #3

    Vanadium 50

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    Look at the BF's - they are equal for p pi0 and n pi+, so we're not talking about FCNC loops.

    You have uus --> uud + ddbar (p pi0)
    and uus --> udd + udbar (n pi+)

    This is just a rearrangement, which explains their equality.
     
  5. Oct 6, 2011 #4
    Thanks guys. The BF's are actually not 50/50 but 52/48. Why should they be slightly different? Does the fact that alpha for p pi0 (36 deg) and for n pi+ (167 deg) relevant for this? Appreciate your comments.
     
  6. Oct 6, 2011 #5

    Vanadium 50

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    The masses aren't identical for n and p, nor pi+ and pi0.
     
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