Precise measurement of the e+ e-→π+ π-(γ) cross section with the initial-state radiation method at BABAR

Abstract

A precise measurement of the cross section of the process e +e -→π +π -(γ) from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using 232fb -1 of data collected with the BABAR detector at e +e - center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process e +e -→μ +μ -(γ) γ ISR, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e +e -→π +π -(γ) is obtained with a systematic uncertainty of 0.5% in the dominant ρ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured ππ cross section from threshold to 1.8GeV is (514.1±2.2(stat)±3.1(syst))×10 -10. © 2012 American Physical Society.