The discrepancy between τ and e+e− spectral functions revisited and the consequences for the muon magnetic anomaly
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- Davier, M., Hoecker, A., López Castro, G. et al. Eur. Phys. J. C (2010) 66: 127. doi:10.1140/epjc/s10052-009-1219-4
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We revisit the procedure for comparing the ππ spectral function measured in τ decays to that obtained in e+e− annihilation. We re-examine the isospin-breaking corrections using new experimental and theoretical input and find improved agreement between the τ−→π−π0ντ branching fraction measurement and its prediction using the isospin-breaking-corrected e+e−→π+π− spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g−2 using e+e− and τ data with the new corrections and find a reduced difference between the two evaluations. The new tau-based estimate of the muon magnetic anomaly is found to be 1.9 standard deviations lower than the direct measurement.