Observation of e+e- --> rho+rho- near sqrt(s)=10.58 GeV

We report the first observation of $e^+e^- \\to \\rho^+\\rho^-$, in a data sample of 379 $fb^{-1}$ collected with the BABAR detector at the {PEP-II} $e^+e^-$ storage ring at center-of-mass energies near $\\sqrt{s} = 10.58 GeV. We measure a cross section of $\\sigma({e^+e^-\\} \\to \\rho^+ \\rho^-) = {19.5 \\pm 1.6(stat) \\pm 3.2(syst) fb}$. Assuming production through single-photon annihilation, there are three independent helicity amplitudes. We measure the ratios of their squared moduli to be $|{F}_{00}|^2 : |{F}_{10}|^2 : |{F}_{11}|^2 = 0.51 \\pm 0.14(stat) \\pm 0.07(syst) : 0.10 \\pm 0.04(stat) \\pm 0.01(syst) : 0.04 \\pm 0.03(stat) \\pm 0.01(syst)$. The $|{F}_{00}|^2$ result is inconsistent with the prediction of 1.0 made by QCD models with a significance of 3.1 standard deviations including systematic uncertainties.