Antimatter-Matter Annihilation (i.e. antiproton w/ positron)

  1. I know that a particle's exact anti-counterpart (i.e. an electron and positron) will annihilate into pure energy. But my question is do differing particles and antiparticles (such as an antiproton and positron) annihilate each other, and if so how much so, because I doubt it too would result in pure energy. I have seen this question pop up a couple times but still have not found any sufficent answer.
     
  2. jcsd
  3. SteamKing

    SteamKing 8,352
    Staff Emeritus
    Science Advisor
    Homework Helper

    Would you expect an electron and a proton to 'annihilate' each other?

    An anti-proton and a positron are both antimatter. Just like an electron could be captured by a proton to form a hydrogen atom, a positron could be captured by an anti-proton to form an atom of anti-hydrogen:

    http://en.wikipedia.org/wiki/Antihydrogen

    Significant production of anti-hydrogen is hampered by the fact that it is easy for this material to interact with matter and annihilate itself before significant quantities can be accumulated.
     
  4. Bill_K

    Bill_K 4,160
    Science Advisor

    There is no such thing as "pure energy". Energy is a property that particles have. When a particle and its antiparticle annihilate, they turn into other particles, usually photons. The rest mass of the original particles becomes the energy carried by the photons.
     
  5. 1. If the particles+antiparticles are fundamental then No, there's no reason for them to annihilate... it would in general violate some symmetries.
    2. If they are not fundamental but composite, then yes, why not? You just need to give them enough energy so that the constituents would see each other... for example take:
    neutron+antiproton...
    in general there wouldn't be a reason for them to annihilate.
    in quark level though, they have same pairs of quark-antiquark:
    [itex] udd + \bar{u}\bar{u}\bar{d} [/itex]
     
  6. mfb

    Staff: Mentor

    Neutron+antiproton has to generate at least one charged particle, most likely a (negatively) charged pion, to conserve the total charge.

    In general, annihilations of baryons (like neutron and proton) with antibaryons produce multiple pions and not just photons. Mixing things like electrons (matter) with antibaryons won't lead to annihilation, as there is no process that satisfies all conservation laws (here for example: the baryon number).
     
  7. Or maybe it just won´t be annihilation?

    Consider the opposite - mixing positrons (antimatter) with baryons.

    A process like
    n+e+->p+nu~e
    satisfies all conservation laws. But would you call it annihilation?

    Also, does it mean that electron and positive muon cannot annihilate because it would violate the conservation of electron and muon charges? Or does it? Is the process
    e+μ+->nue+nu~μ
    possible? And is it annihilation?
     
  8. mfb

    Staff: Mentor

    No.

    It is possible, but extremely unlikely. See this thread for a discussion. Even in a bound state (muonium), the branching fraction is less than 1 in a billion. There is a planned experiment to search for this decay: presentation. The experimental signature would just be vanishing muonium.
     
  9. Effectively, a positive muon like many nuclei of nucleons has a choice between positron emission and electron capture. Correct?

    Can the branching ratios and half lives for positron emission and electron capture be predicted?
     
  10. mfb

    Staff: Mentor

    It has some similarity, yes.
    See the second link in my previous post. I'm not sure where the deviations between the predictions come from, but they all agree that the "electron capture" process is extremely rare.
     
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