Physics – High Energy Physics – High Energy Physics - Experiment
Scientific paper
2003-12-31
Physics
High Energy Physics
High Energy Physics - Experiment
9 pages, 7 figures, proceedings of the SIGHAD03 workshop (Pisa, October 2003) on e+e- annihilation cross sections at low energ
Scientific paper
10.1016/S0920-5632(04)00028-3
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 \ee annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between \ee and $\tau$ spectral functions in the $\pi\pi$ channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and $1.0 {\rm GeV}/c^2$.The deviations from the measurement at BNL are found to be $(22.1 \pm 7.2 \pm 3.5 \pm 8.0)~10^{-10}$ (1.9 $\sigma$) and $(7.4 \pm 5.8 \pm 3.5 \pm 8.0)~10^{-10}$ (0.7 $\sigma$) for the \ee- and $\tau$-based estimates, respectively, where the second error is from the nonhadronic contributions and the third one from the BNL measurement. Taking into account the $\rho^- - \rho^0$ mass splitting determined from the measured spectral functions increases the $\tau$-based estimate and leads to a worse discrepancy between the two estimates.
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