Abstract
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e + e − annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e + e − and T spectral functions in the ππ channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and 1.0 GeV/ c 2.The deviations from the measurement at BNL are found to be (22.1 ± 7.2 ± 3.5 ± 8.0) 10 −10 (1.9 σ) and (7.4±5.8 ± 3.5 ± 8.0) 10 −10 (0.7 σ) for the e + e − and τ-based estimates, respectively, where the second error is from the nonhadronic contributions and the third one from the BNL measurement. Taking into account the ρ − ρ 0 mass splitting determined from the measured spectral functions increases the τ-based estimate and leads to a worse discrepancy between the two estimates.
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