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Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR (1205.2228v1)

Published 10 May 2012 in hep-ex

Abstract: A precise measurement of the cross section of the process $e+e-\to\pi+\pi-(\gamma)$ 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 $e+e-\to\mu+\mu-(\gamma)\gamma_{\rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e+e-\to\pi+\pi-(\gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $\rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $\pi\pi$ cross section from threshold to 1.8GeV is $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10{-10}$.

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