Cross section of the η′→γγ decay

[zihao yu]

Is there any measure for cross section of η′→γγ? Or has anyone did the calculation??

 

[Orodruin]

That is a decay, decays have decay rates, not cross sections.

 

[dukwon]

The PDG averages for the partial width of $\eta^\prime \to \gamma \gamma$ is $4.28\pm0.19~\rm{keV}$, and the branching fraction is $2.00\pm0.15\%$
http://pdglive.lbl.gov/BranchingRatio.action?parCode=M002&desig=6

I don't know how you'd go about calculating these things.