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 RennieCommented Mar 22, 2014 at 11:26
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$\begingroup$ Aha! This is the answer I was thinking of. $\endgroup$– John RennieCommented Mar 22, 2014 at 11:29
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1 Answer
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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.
answered Mar 21, 2014 at 20:27
dmckee --- ex-moderator kittendmckee --- ex-moderator kitten
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$\begingroup$ I know but that was not my question. Sorry for the misleading formulation. $\endgroup$ Commented Mar 21, 2014 at 20:41