Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
2003-10-15
Phys.Lett.B583:222-230,2004
Physics
High Energy Physics
High Energy Physics - Phenomenology
11 pages, Latex, 1 table, 3 figures; update: several points described in more detail, slightly shifted fit parameters (Tab.1),
Scientific paper
10.1016/j.physletb.2004.01.021
We study possible so far unaccounted isospin breaking effects in the relation between the pion form factor as determined in e^+e^- experiments and the corresponding quantity obtained after accounting for known isospin breaking effects by an isospin rotation from the tau--decay spectra. In fact the observed 10% discrepancy in the respective pion form factors may be explained by the isospin breaking which is due to the difference between masses and widths of the charged and neutral rho mesons. Since the hadronic contribution to the muon anomalous magnetic moment can be calculated directly in terms of the e^+e^- - data the corresponding evaluation seems to be more reliable. Our estimate is a_mu(had)=694.8(8.6) x 10^{-10}. The tau - data are usefull at the presently aimed level of accuracy only after appropriate input from theory.
Ghozzi Stéphane
Jegerlehner Fred
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