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Description:
We present a dispersive representation of the η′ transition form factor that allows one to account, in a consistent way, for the effects of ρ–ω mixing in both the isoscalar and the isovector contributions. Using this formalism, we analyze recent data on η′→π+π−γ to constrain the isovector part of the form factor, individually and in combination with data for the pion vector form factor, which suggests a tension in the ρ–ω mixing parameter. As a first application, we use our results, in combination with the most recent input for the isoscalar part of the form factor, to predict the corresponding spectrum of η′→ℓ+ℓ−γ, in particular we find the slope parameter bη′=1.455(24)GeV−2. With forthcoming data on the latter process, our results establish the necessary framework to improve the evaluation of the η′-pole contribution to the anomalous magnetic moment of the muon using experimental input from both η′ decay channels.