Antimatter - Antigravity LHC Results

Discussion in 'Physics & Math' started by danshawen, May 25, 2017.

  1. exchemist Valued Senior Member

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    This raises a question in my mind that I can't answer and I wonder if anybody knowledgeable may be able to help me with. What is the QM process of annihilation between an electron and a positron and how does this give rise to EM radiation?

    I was thinking that we all learnt at university about transition dipole moment when an electron changes state in an atom, how this is associated with emission or absorption of a photon, how the symmetry of the process results in selection rules for transitions, and so on. What kind of interaction between the wavefunction of an electron and a positron occurs and how does this lead to generation of a photon? Presumably there must be some sort of transition dipole moment produced (related to the opposite charges I presume), a symmetry change and an angular momentum change, which are satisfied by emission of a photon. I had a quick look on the web but could not find anything obvious on the subject. Can anyone point me to a good source? I'm not looking for walls of Greek, just a short summary.
     
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  3. The God Valued Senior Member

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    Dont be mean.

    Hansda's insistence on anti-wave was improper understanding of wave particle duality, simple formulation suggests h/p and p (momentum: recall we talked about this in ref to Q-reeus link) has no special functionality wrt antimatter. My responses was guided kind of expecting that he would realize, but I never knew that you would also be having same doubts. Origin intervened and stated the definition nicely.
     
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  5. river Valued Senior Member

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    Why not contact the Perimeter Institute for Theoretical Physics in Waterloo Ontario , Canada

    Website

    www.perimeterinstitute.ca

    With your thinking ? You can contact them , when you get to this website .
     
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  7. exchemist Valued Senior Member

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    I wasn't actually, as my own reply at the time indicates. But you would do better to help with a positive contribution on these occasions - if you can make one - rather than hinting that you know the answer to the problem while keeping it to yourself.

    Anyway, I'm more interested now in what I do not in fact understand about the annihilation process - see my latest post. I am not expecting you to contribute to answering that, by the way.
     
  8. river Valued Senior Member

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    In my post#83

    Good suggestion ,
     
  9. river Valued Senior Member

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    Exchemist is missing .
     
  10. Q-reeus Valued Senior Member

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    Won't attempt an answer in terms of wavefunctions, but have you checked the main answer here?:
    https://physics.stackexchange.com/q...-what-direction-are-the-photons-released?rq=1
    Last part re positronium formation suggests a general dynamical progression.
    Given the 'point' nature of electrons and positrons, and positional uncertainty implied by the de Broglie relation, there will never be a truly exact head on collision. Hence, the two will (maybe only very briefly) always develop some orbital angular momentum, which all by itself results in a rotating dipole moment. Heuristically one expects the lifetime should be shorter the closer to what passes for dead-on are the initial trajectories, since the orbital angular momentum hence rotational period is then less. A little like how it is with classical GW emission from 'BH binary' inspiral, reduced moment is more than compensated by increased angular frequency re radiated power. In the QED picture, that will translate into joint gamma rays emission probability. Hand-wavy I know. Full QED treatment would no doubt require that wall of Greek.
     
  11. exchemist Valued Senior Member

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    Thanks for this. The link, which I had not seen, appears preoccupied with something else, viz. angle and energy of the photons. But your remarks about positronium (or a fleeting pseudo-positronium) are interesting, as are the remarks in the link about the "de Broglie size" of the particles, depending on their momentum. I wonder if the close approach of the 2 opposite charges in itself provides a transition dipole moment, regardless of any rotational charge motion there may be. Could that be possible? I suppose the symmetry and angular momentum issue is taken care of by the fact it is an opposed pair of photons that gets released.
     
  12. The God Valued Senior Member

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    I very specifically asked about this process in our recent exchange and you gave an impression that it was well understood and not a big deal.

    But anyway good that you have also raised question on this. Actually there is no known process. It is served that matter and antimatter annihilate.
     
  13. exchemist Valued Senior Member

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    Haha very funny. You don't have a clue what Q-reeus and I are talking about.

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  14. The God Valued Senior Member

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    Again you are being mean.

    You had objected to relative momentum requirement for particle anti particle annihilation. Now you are indulging into the possibility of dipole formation just before annihilation!! Very sweet.

    But I am impressed and I can foresee that you will end up with more doubts in your head regarding this annihilation process. Unless of course you pretend to understand.
     
  15. exchemist Valued Senior Member

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    Indulging? There must be a transition dipole moment or some such process to generate a photon (or pair of them). Unless I suppose it is better thought of in terms of synchrotron radiation from abruptly decelerating charged particles or something. And with a pair of opposite charges approaching, there is clearly a basis for either, but I would like to know the mechanism, if it can be simply explained. Wanting to know more about this is nothing to do with"doubt". It is just that it is not part of chemistry, you see, so I never learned it. But I am here to learn, from those with the requisite knowledge and patience. Q-reeus is a good source, I find, as I'm sure you would agree from your own experience of learning here.
     
  16. The God Valued Senior Member

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    Q-reeus contribution here is acknowledged.

    Dipole has ample reference in chemistry, so the concept is not alien to a person of Chemistry background.

    Without a stable spatial separation, utility of dipole may not be very useful. Depending on the relative approach motion between both the particles, the pre collapse trajectory will be determined, which may give a transient dipole structure. But we are certainly not talking about some stable binary formation here, the question is more about annihilation post collision.
     
  17. exchemist Valued Senior Member

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    There is no stable spatial separation in a transition dipole moment.
     
  18. The God Valued Senior Member

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    That's what I am saying...Did I say smthing diffetent?
     
  19. Q-reeus Valued Senior Member

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    It all gets way out of my league when QFT details come into play. Best I can summarize is that at low energies it evidently makes sense to talk of electron-positron dipole moments and so on. But at high incident energies the language gets more into excitation of various vacuum fields and all the complexities of SM rear their ugly head.
    One thing new to me was the role of spin in positronium states allowing 3-photon or 5-photon etc emissions: https://en.wikipedia.org/wiki/Positronium
     
  20. hansda Valued Senior Member

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    Consider wave-form of a particle(say electron) and wave-form of its antiparticle(positron). Are both these wave-form same?
     
  21. The God Valued Senior Member

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    So you did not refer to wave definition.
    Refer to easy to read wiki link at
    https://en.m.wikipedia.org/wiki/Wave

    You can jump to quantum mechanical wave, you may like to read a bit about wave function here. I do not think you will get a separate category as anti-wave.
     
  22. hansda Valued Senior Member

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    Answer my question at post #97, in YES or NO.
     
  23. exchemist Valued Senior Member

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    As far as I can see, the form of the wave function for an antiparticle is related to that of the particle through quite advanced QM such as Dirac's equation (Schroedinger's does not deal with spin for instance so that won't do).

    There is something here that may help, see esp. Equations 7a and 7b, in which the form is related, one containing a -ve exponent and one a +ve one: https://www.researchgate.net/publication/242378812_BEGINNER'S_GUIDE_TO_PARTICLE_-_ANTIPARTICLE

    There is an interesting discussion (in not very good English), explaining the +ve and -ve exponents as corresponding to +ve and -ve energy, later interpreted as particle and antiparticle. I had never seen this before (Dirac's equation having been out of scope for us chemists at uni) so thanks for the question.

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