2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/37578We have observed the rare decay B0->rho+rho- in a sample of 89 million BBbar pairs recorded with the BABAR detector. We measure the branching fraction B(B0->rho+rho-)=(27+7-6+5-7)10^-6 and determine the longitudinal polarization fraction Gamma_L/Gamma=0.99+0.01-0.07+-0.03. Our results are preliminary.15 pages, 8 postscript figures, Contributed to the XXIst International Symposium on Lepton and Photon Interactions at High Energies, 8/11 - 8/16/2003, Fermilab, Illinois USAHigh Energy Physics - Experimenttext