Adachi, I.Aggarwal, L.Aihara, H.Akopov, N.Aloisio, A.Anh Ky, N.Asner, D.M.Atmacan, H.Aushev, V.Aversano, M.Ayad, R.Babu, V.Bae, H.Bahinipati, S.Bambade, P.Banerjee, S.Bansal, S.Barrett, M.Baudot, J.Baur, A.et al.2025-05-132025-05-132024Physical Review D (particles, fields, gravitation, and cosmology), 2024; 110(11):112005-1-112005-252470-00102470-0029https://hdl.handle.net/2440/144512We report a measurement of the eþe− → πþπ−π0 cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an eþe− data sample corresponding to 191 fb−1 of integrated luminosity, collected at a center-of-mass energy at or near the ϒð4SÞ resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in eþe− → πþπ−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 a3π μ ¼ ½48.91 0.23ðstatÞ 1.07ðsystÞ × 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.enPublished by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3 .Particle interactions; Particle production; Light mesons; Lepton collidersJournal article10.1103/physrevd.110.112005723477De La Motte, S.A. [0000-0003-3905-6805]