Measurement of the e+e− → π+π−π0 cross section in the energy range 0.62–3.50 GeV at Belle II

We report a measurement of the e⁺e⁻ → π⁺π⁻π⁰ cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an e⁺e⁻ data sample corresponding to 191 fb⁻¹ of integrated luminosity, collected at a center-of-mass energy at or near the ϒ(4S) resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in e⁺e⁻ → π⁺π⁻π⁰γ events, which involve a π⁰ → γγ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the ω and ϕ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62–1.80 GeV energy range yield a^3πμ = [48.91 ± 0.23(stat) ± 1.07(syst)] × 10⁻¹⁰ for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by 2.5 standard deviations from the most precise current determination.

Duke Scholars

Author Anselm G. Vossen Physics