The Hadronic Contribution to (g − 2)µ
نویسنده
چکیده
The evaluation of the hadronic contribution to the muon magnetic anomaly aμ is revisited, taking advantage of new experimental data on ee annihilation into hadrons: SND and CMD-2 for the ππ channel, and BABAR for multihadron final states. Discrepancies are observed between KLOE and CMD-2/SND data, preventing one from averaging all the ee results. The long-standing disagreement between spectral functions obtained from τ decays and ee annihilation is still present, and not accounted by isospin-breaking corrections, for which new estimates have been presented. The updated Standard Model value for aμ based on e + e − annihilation data is now reaching a precision better than experiment, and it disagrees with the direct measurement from BNL at the 3.3σ level, while the τ -based estimate is in much better agreement. The τ/ee discrepancy, best revealed when comparing the measured branching fraction for τ− → ππντ to its prediction from the isospin-breaking-corrected
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