2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207336We have observed the rare decay B0 => rho+ rho- in a sample of 89 million BB pairs recorded with the BABAR detector. The number of observed events is 88 +23-21 +-9, with a significance of 5.1 standard deviations with systematic uncertainties included. The branching fraction and the longitudinal polarization are measured to be BR(B0 => rho+ rho-) = (25 +7-6 +5-6)*10^{-6} and Gamma_L/Gamma = 0.98 +0.02-0.08 +-0.03, respectively.8 pages, 3 postscript figues, submitted to Phys. Rev. D (Rapid Communications)High Energy Physics - Experimenttext