Updated estimate of the muon magnetic moment using revised results from e+e- annihilation

TL;DR

This paper provides an updated estimate of the muon magnetic moment's hadronic contribution, incorporating recent reanalyses of e+e- annihilation data, which improves agreement with tau spectral functions but still shows some discrepancies.

Contribution

It offers a revised calculation of the muon g-2 using new e+e- data and analyzes the impact of spectral function differences on the estimate.

Findings

Improved agreement between e+e- and tau spectral functions in the ππ channel.

Discrepancies remain between 0.85 and 1.0 GeV/c^2 energy range.

Updated estimates show a 1.9 sigma deviation from BNL measurements.

Abstract

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.