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Physical Review D 86 (2012) 032013
Precise Measurement of the e+ e- --> pi+ pi- (gamma) Cross Section with the Initial-State Radiation Method at BABAR
J. P. Lees1, V. Poireau1, V. Tisserand1, D. Bernard2, M. Verderi2, N. Arnaud3, M. Davier3, D. Derkach3, G. Grosdidier3, F. Le Diberder3, A. M. Lutz3, B. Malaescu3, P. Roudeau3, M. H. Schune3, A. Stocchi3, L. L. Wang3, G. Wormser3, S. Akar4, E. Ben-Haim4, M. Bomben4, G. R. Bonneaud4, H. Briand4, G. Calderini4, J. Chauveau4, O. Hamon4, Ph. Leruste4, G. Marchiori4, J. Ocariz4, S. Sitt4, S. Emery5, G. Hamel de Monchenault5, G. Vasseur5, Ch. Yeche5
For the BABAR collaboration(s)
(2012)

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 $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.
1:  LAPP - Laboratoire d'Annecy le Vieux de Physique des Particules
2:  LLR - Laboratoire Leprince-Ringuet
3:  LAL - Laboratoire de l'Accélérateur Linéaire
4:  LPNHE - Laboratoire de Physique Nucléaire et de Hautes Énergies
5:  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
Physics/High Energy Physics - Experiment
Fulltext link: 
http://fr.arXiv.org/abs/1205.2228