Reevaluation of the Hadronic Contributions to the Muon g-2 and to alpha(MZ)

TL;DR

This paper reevaluates the hadronic contributions to the muon g-2 and the electromagnetic coupling at the Z-boson mass, incorporating new data and methods, resulting in decreased contributions and implications for the Higgs boson mass.

Contribution

It provides a revised, more precise calculation of hadronic effects on muon g-2 and alpha(MZ), using updated experimental data and improved analysis techniques.

Findings

Lower hadronic contributions compared to previous estimates.

Discrepancy of 3.6 sigma and 2.4 sigma between Standard Model and experimental muon g-2.

Updated value for Delta_alpha_had at MZ with reduced uncertainty.

Abstract

We reevaluate the hadronic contributions to the muon magnetic anomaly, and to the running of the electromagnetic coupling constant at the Z-boson mass. We include new pi+pi- cross-section data from KLOE, all available multi-hadron data from BABAR, a reestimation of missing low-energy contributions using results on cross sections and process dynamics from BABAR, a reevaluation of all experimental contributions using the software package HVPTools, together with a reanalysis of inter-experiment and inter-channel correlations, and a reevaluation of the continuum contributions from perturbative QCD at four loops. These improvements lead to a decrease in the hadronic contributions with respect to earlier evaluations. For the muon g-2 we find lowest-order hadronic contributions of (692.3 +- 4.2) 10^-10 and (701.5 +- 4.7) 10^-10 for the e+e- based and tau-based analyses, respectively, and full Standard Model predictions that differ by 3.6 sigma and 2.4 sigma from the experimental value. For the e+e- based five-quark hadronic contribution to alpha(MZ) we find Delta_alpha_had[5](MZ)=(275.7 +- 1.0) 10^-4. The reduced electromagnetic coupling strength at MZ leads to an increase by 7 GeV in the most probable Higgs boson mass obtained by the standard Gfitter fit to electroweak precision data.