UC Berkeley

We report the first observation of e+e-→ρ+ρ-, in a data sample of 379fb-1 collected with the BABAR detector at the PEP-II e+e- storage ring at center-of-mass energies near s=10.58GeV. We measure a cross section of σ(e+e-→ρ+ρ-)=8.3±0.7(stat)±0.8(syst)fb within the range of |cos θ*|<0.8 and |cos θ±|<0.85, where θ* is the center-of-mass polar angle of the ρ± meson and θ± are the angles in the ρ± rest frame between the direction of the boost from the laboratory frame and the direction of the π±. Assuming production through single-photon annihilation, there are three independent helicity amplitudes. We measure the ratios of their squared moduli to be |F00|2|F10|2|F11|2=0.51±0.14(stat)±0.07(syst)0. 10±0.04(stat)±0.01(syst)0.04±0.03(stat)±0.01(syst). The |F00|2 result is inconsistent with the prediction of 1.0 made by QCD models with a significance of 3.1 standard deviations including systematic uncertainties. © 2008 The American Physical Society.