The Discrepancy Between tau and e+e- Spectral Functions Revisited and the Consequences for the Muon Magnetic Anomaly

M. Davier (1) , A. Hoecker (2) , G. Lopez Castro , B. Malaescu (1) , X. H. Mo (3) , G. Toledo Sanchez , P. Wang (3) , C. Z. Yuan (3) , Z. Zhang (1)

1 LAL - Laboratoire de l'Accélérateur Linéaire
2 CERN - European Organization for Nuclear Research
3 IHEP - Institute of High Energy Physics

We revisit the procedure for comparing the pi pi spectral function measured in tau 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 tau- --> pi- pi0 nu_tau branching fraction measurement and its prediction using the isospin-breaking-corrected e+e- --> pi+pi- spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g-2 using e+e- and tau 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.

Domaines: Physique des Hautes Energies - Phénoménologie [hep-ph]

M. Davier, A. Hoecker, G. Lopez Castro, B. Malaescu, X. H. Mo, et al.. The Discrepancy Between tau and e+e- Spectral Functions Revisited and the Consequences for the Muon Magnetic Anomaly. European Physical Journal C: Particles and Fields, 2010, 66, pp.127-136. ⟨10.1140/epjc/s10052-009-1219-4⟩. ⟨in2p3-00455617⟩