About pair production using light

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Summary:
Can light make two pairs? (assuming enough energy to make two pairs)
If so, why?
Can light make two pairs? (assuming enough energy to make two pairs)
If so, why? or If not, why not?
 

Answers and Replies

  • #2
Baluncore
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Welcome to PF.
Two pairs of what?
 
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Welcome to PF.
Two pairs of what?
Thank you~ (electron+electron+positron+positron)!!
 
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PeroK
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Thank you~ (electron+electron+positron+positron)!!
Whence these pairs?
 
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Whence these pairs?
I don't understand. What's mean "Whence"?
 
  • #10
phinds
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in a book
That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".
 
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That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".
Sorry.. The book is Concepts of Modern Physics. I was not good at English and citation.
 
  • #12
PeroK
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in a book: Electromagnetic waves (with enough energy) = γe− + e+
in my opinion: Electromagnetic waves (with enough energy) = γe− + e+ that's right! or Electromagnetic waves (with enough energy) = γe− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.
This pair production can only take place in the presence of an atom of molecule - which is required to balance momentum. I don't know why precisely only one pair may be produced - I'm sure someone will answer that - but it's not enough just to say that energy and momentum are conserved. There must be a possible interaction between the photon and the atom that produces two pairs.
 
  • #13
vela
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in a book: Electromagnetic waves (with enough energy) = γe− + e+
in my opinion: Electromagnetic waves (with enough energy) = γe− + e+ that's right! or Electromagnetic waves (with enough energy) = γe− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.
You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.
 
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You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.
Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photons
 
  • #15
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Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photons
If the answer to my question is yes, where can I find the relevant concept or data?
 
  • #16
PeroK
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You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.
This is a different process: this is pair production from a pair of photons. It's the reverse of pair annhililation.

An electron-positron pair can annhililate and produce an even number of photons; but, I'm not sure that two photons could produce more than one electron-positron pair. I suspect that you can only get one electron-positron pair per pair of photons.

And similarly in the case of pair production from a single photon where the interaction involves additionally an atom or molecule.
 
  • #17
vela
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This is a different process: this is pair production from a pair of photons. It's the reverse of pair annhililation.
It's essentially the same process. It's just that in the case involving a nucleus, the second photon is a virtual photon from the interaction of the photon with the nucleus.

An electron-positron pair can annihilate and produce an even number of photons; but, I'm not sure that two photons could produce more than one electron-positron pair. I suspect that you can only get one electron-positron pair per pair of photons.

And similarly in the case of pair production from a single photon where the interaction involves additionally an atom or molecule.
It's been a long time since I studied particle physics, but I'll say I think it's possible though I'd expect it to be really unlikely. For example, the neutral pion can decay into two photons, and it can also decay into two electron-positron pairs. So conceivably, two photons could produce a pion, which is simply the reverse of the first decay I mentioned, that then decays into two electrons and two positrons. At the least, this hypothetical scenario suggests no conservation laws are broken which would invalidate the process of two photons producing two pairs.

The simplest scenario which might work is two photons coupling to separate electron-positron pairs and then then one particle from one pair exchanges a virtual photon with a particle from the second pair so that momentum and energy are conserved.
 

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