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

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 $232\invfb$ 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 $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.
Document type :
Journal articles
Physical Review D, American Physical Society, 2012, 86, pp.032013. <10.1103/PhysRevD.86.032013>

http://hal.in2p3.fr/in2p3-00697175
Contributor : Claudine Bombar <>
Submitted on : Monday, May 14, 2012 - 4:52:28 PM
Last modification on : Wednesday, July 20, 2016 - 10:05:24 AM

### Citation

J. P. Lees, V. Poireau, V. Tisserand, D. Bernard, M. Verderi, et al.. Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR. Physical Review D, American Physical Society, 2012, 86, pp.032013. <10.1103/PhysRevD.86.032013>. <in2p3-00697175>

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