A Global Treatment Of VMD Physics Up To The phi: II. tau Decay and Hadronic Contributions To g-2

TL;DR

This paper uses a comprehensive model to fit e+ e- annihilation and tau decay data, improving estimates of hadronic contributions to muon g-2 with reduced uncertainties.

Contribution

It extends a global fit framework to include tau decay spectra and lineshape distortions, providing more accurate estimates of hadronic effects on muon g-2.

Findings

Successful simultaneous fit of e+ e- and tau data.

40% reduction in uncertainty of the pi+ pi- contribution to g-2.

Identification of lineshape distortions in tau spectra from different experiments.

Abstract

Relying on the Hidden Local Symmetry (HLS) model equipped with a mechanism breaking the U(3)/SU(3)/SU(2) symmetries and generating a dynamical vector meson mixing, it has been shown that a global fit successfully describes the cross sections for the e+ e- -> pi+ pi-, e+ e- -> (pi0/eta) gamma and e+ e- -> pi0 pi+ pi- annihilation channels. One extends this global fit in order to include also the dipion spectra from the tau decay, taking into account all reported information on their statistical and systematic errors. A model accounting for lineshape distortions of the rho+- spectrum relative to rho0 is also examined when analyzing the tau data behavior within the global fit framework. One shows that a successful account for e+ e- annihilation data and tau spectra can be simultaneously reached. Then, issues related with non--perturbative hadronic contributions to the muon g-2 are examined in details. It is shown that all e+ e- data considered together allow for improved and motivated estimates for the a_mu(pi+ pi-), the pi+ pi- loop contribution to the muon g-2; for instance, integrated between 0.630 and 0.958 GeV, we find a_mu(pi+ pi-)= 359.62 +- 1.62 (in units of 10^{-10}), a 40% improvement of the current uncertainty. The effects of the various tau samples in the context of a global fit procedure leads to conclude that different lineshape distortions are revealed by the ALEPH, BELLE and CLEO data samples. Relying on global fits to the data quoted above, one also provides motivated estimates of the pi+ pi-, pi0 gamma, eta gamma and pi0 pi+ pi- contributions to a_mu up to 1 GeV with the smallest possible uncertainties. These estimates are based on various global fit configurations, each yielding a good probability.