Abstract
We study the reaction e+e- → π0γ based on a dispersive representation of the underlying π0 → γγ∗ transition form factor. As a first application, we evaluate the contribution of the π0γ channel to the hadronic-vacuum-polarization correction to the anomalous magnetic moment of the muon. We find aμπ0γ|≤1.35 GeV = 43.8(6) × 10-11 , in line with evaluations from the direct integration of the data. Second, our fit determines the resonance parameters of ω and ϕ . We observe good agreement with the e+e- → 3π channel, explaining a previous tension in the ω mass between π0γ and 3π by an unphysical phase in the fit function. Combining both channels we find M¯ω = 782.736(24) MeV and M¯ϕ = 1019.457(20) MeV for the masses including vacuum-polarization corrections. The ϕ mass agrees perfectly with the PDG average, which is dominated by determinations from the K¯K channel, demonstrating consistency with 3π and π0γ . For the ω mass, our result is consistent but more precise, exacerbating tensions with the ω mass extracted via isospin-breaking effects from the 2π channel.