The discussion centers on the feasibility of pair production using light, specifically whether a single photon can create two electron-positron pairs. Participants conclude that while pair production is a fundamental process in Quantum Electrodynamics (QED), typically represented as γ + γ → e⁻ + e⁺, a single photon generally produces only one pair due to conservation laws. The presence of an atom or molecule is necessary to balance momentum during this process. Higher-order interactions may allow for multiple pairs from multiple photons, but such occurrences are rare.
PREREQUISITESPhysicists, students of particle physics, and anyone interested in the principles of light-matter interactions and pair production processes.
Thank you~ (electron+electron+positron+positron)!Baluncore said:Welcome to PF.
Two pairs of what?
Whence these pairs?wasong said:Thank you~ (electron+electron+positron+positron)!
I don't understand. What's mean "Whence"?PeroK said:Whence these pairs?
Whence: from what place, source or cause.wasong said:I don't understand. What's mean "Whence"?
Why?? There's no problem if you keep Conservation of energy and conservation of charge, right?Baluncore said:It appears that only one pair can be created by one photon.
https://en.wikipedia.org/wiki/Pair_production
in a book: Electromagnetic waves (with enough energy) = γ→ e− + e+PeroK said:
That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".wasong said:in a book
Sorry.. The book is Concepts of Modern Physics. I was not good at English and citation.phinds said:That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".
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.wasong said:in a book: Electromagnetic waves (with enough energy) = γ→ e− + e+
in my opinion: Electromagnetic waves (with enough energy) = γ→ e− + e+ that's right! or Electromagnetic waves (with enough energy) = γ→ e− + 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.wasong said:in a book: Electromagnetic waves (with enough energy) = γ→ e− + e+
in my opinion: Electromagnetic waves (with enough energy) = γ→ e− + e+ that's right! or Electromagnetic waves (with enough energy) = γ→ e− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.
Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photonsvela said: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.
If the answer to my question is yes, where can I find the relevant concept or data?wasong said:Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photons
This is a different process: this is pair production from a pair of photons. It's the reverse of pair annhililation.vela said: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.
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.PeroK said:This is a different process: this is pair production from a pair of photons. It's the reverse of pair annhililation.
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.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.