Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e + e −→π + π − cross section data from BABAR

Using recently published, high-precision π + π − cross section data by the BABAR experiment from the analysis of e + e − events with high-energy photon radiation in the initial state, we reevaluate the lowest order hadronic contribution (aμhad,LO) to the anomalous magnetic moment of the muon. We employ newly developed software featuring improved data interpolation and averaging, more accurate error propagation and systematic validation. With the new data, the discrepancy between the e + e −- and τ-based results for the dominant two-pion mode reduces from previously 2.4σ to 1.5σ in the dispersion integral, though significant local discrepancies in the spectra persist. We obtain for the e + e −-based evaluation aμhad,LO=(695.5±4.1)× 10⁻¹⁰ , where the error accounts for all sources. The full Standard Model prediction of a μ differs from the experimental value by 3.2σ.