Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e+e- -> pi+pi- cross section data from BABAR

TL;DR

This paper reevaluates the hadronic contribution to the muon magnetic anomaly using new high-precision e+e- -> pi+pi- data from BABAR, reducing discrepancies between different data sources and refining the Standard Model prediction.

Contribution

It introduces improved software for data analysis and provides a more accurate reevaluation of the hadronic contribution to the muon g-2, reducing previous discrepancies.

Findings

Reduced discrepancy between e+e- and tau-based results from 2.4 sigma to 1.5 sigma.

Calculated a_mu[had,LO] = (695.5 +- 4.1) x 10^-10.

Standard Model prediction differs from experiment by 3.2 sigma.

Abstract

Using recently published, high-precision pi+pi- cross section data by the BABAR experiment from the analysis of e+e- events with high-energy photon radiation in the initial state, we reevaluate the lowest order hadronic contribution a_mu[had,LO] to the anomalous magnetic moment of the muon. We employ newly developed software featuring improved data interpolation and averaging, more accurate error propagation and systematic validation. With the new data, the discrepancy between the e+e- and tau-based results for the dominant two-pion mode reduces from previously 2.4 sigma to 1.5 sigma in the dispersion integral, though significant local discrepancies in the spectra persist. We obtain for the e+e- based evaluation amu[had,LO] = (695.5 +- 4.1) 10^-10, where the error accounts for all sources. The full Standard Model prediction of a_mu differs from the experimental value by 3.2 sigma.