Hadronic vacuum polarization and vector-meson resonance parameters from e+e- → π0γ

We study the reaction e(+)e(-) -> pi(0)gamma based on a dispersive representation of the underlying pi(0) -> gamma gamma* transition form factor. As a first application, we evaluate the contribution of the pi(0)gamma channel to the hadronic-vacuumpolarization correction to the anomalous magnetic moment of the muon. We find a(mu)(pi 0)gamma vertical bar(<= 1.35 GeV) = 43.8(6) x 10(-11), in line with evaluations from the direct integration of the data. Second, our fit determines the resonance parameters of. and phi. We observe good agreement with the e(+)e(-) -> 3 pi channel, explaining a previous tension in the omega mass between pi(0)gamma and 3 pi by an unphysical phase in the fit function. Combining both channels we find (M) over bar (omega) = 782.736(24) MeV and (M) over bar (phi) = 1019.457(20) MeV for themasses including vacuumpolarization corrections. The phi mass agrees perfectly with the PDG average, which is dominated by determinations from the (K) over barK channel, demonstrating consistency with 3 pi and pi(0)gamma For the omega mass, our result is consistent but more precise, exacerbating tensions with the omega mass extracted via isospinbreaking effects from the 2 pi channel.