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Electron-pozitron annihilation, conservation of spin

  1. Aug 21, 2009 #1
    I have one question. The most probability annihilation is e+ + e- -> y + y with spins -1/2+1/2=-1+1. But I heard, so, there exist with small probability other combinations of spin. yy is general spin-2 and e+e- is spin-1 and now there is something purportedly with orbitals s, p, d, but I don´t know what, and its my qustion.
  2. jcsd
  3. Aug 21, 2009 #2
    I think you really need to read up on spin. First of all [tex] e^+ + e^- \rightarrow 2 \gamma \text{ or } 3 \gamma[/tex] has either 0 or 1 total spin initially (due to spin statistics). Therefore, if they are in the singlet state initially (S=0) they can go to the [tex] 2\gamma[/tex] final state. If they are in the triplet state initially (S=1) they can proceed to the [tex] 3 \gamma [/tex] final state.
  4. Aug 22, 2009 #3
    Hi Naake-
    As pointed out by Norman, positronium can have the two fermions in either a triplet state or singlet state. Their lifetimes are triplet state (142 nanosecond lifetime, 3 photon decay) or singlet state (125 picosecond lifetime, 2 photon decay). The probability ratio of triplet to singlet states is about 3:1.
    Bob S
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