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What is the most precise data for neutron-antineutron production by one photon (hitting a target in the laboratory system)?

and/or

What is the most precise data for neutron-antineutron annihilation to two photons? Is this data available online?

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  • $\begingroup$ Bearing in mind that the neutron is a composite of quarks and gluons the neutron-antineutron reaction is going to be exceedingly messy. The probability that it will produce just two photons is vanishingly small. I'm sure Anna posted experimental data on proton-antiproton products in an answer (and it was messy) but I can't find the question ... $\endgroup$ – John Rennie Mar 22 '14 at 11:26
  • $\begingroup$ Aha! This is the answer I was thinking of. $\endgroup$ – John Rennie Mar 22 '14 at 11:29
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There is no process $ \gamma \to n $ at all, nor $ \gamma \to n \bar{n}$ with an on-shell photon. The first violated multiple quantum number conservation rules and the second conservation of four-momentum.

The two-photon process

$$ \gamma + \gamma \to n + \bar{n} \,,$$

has allowed quantum numbers but will be exceedingly rare.


It is worth noting that photons do no "annihilate" in the usual sense, and two photon processes imply multiple interaction vertexes.

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  • $\begingroup$ I know but that was not my question. Sorry for the misleading formulation. $\endgroup$ – ClassicalPhysicist Mar 21 '14 at 20:41

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