Eur. Phys. J. C (2010) 66: 1-9
https://doi.org/10.1140/epjc/s10052-010-1246-1

Regular Article - Experimental Physics

Reevaluation of the hadronic contribution to the muon magnetic anomaly using new e ⁺ e ⁻→π ⁺ π ⁻ cross section data from BABAR

¹ Laboratoire de l’Accélérateur Linéaire, IN2P3/CNRS, Université Paris-Sud 11, Orsay, France
² CERN, 1211, Geneva 23, Switzerland
³ Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China

^* e-mail: malaescu@lal.in2p3.fr

Received: 2 September 2009
Revised: 17 November 2009
Published online: 5 February 2010

Abstract

Using recently published, high-precision π ⁺ π ⁻ 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 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 τ-based results for the dominant two-pion mode reduces from previously 2.4σ to 1.5σ in the dispersion integral, though significant local discrepancies in the spectra persist. We obtain for the e ⁺ e ⁻-based evaluation , where the error accounts for all sources. The full Standard Model prediction of a _μ differs from the experimental value by 3.2σ.