# Neutron-Antineutron creation/annihilation data

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?

• 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 ... – John Rennie Mar 22 '14 at 11:26
• Aha! This is the answer I was thinking of. – John Rennie Mar 22 '14 at 11:29

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