We have observed the rare decay B0 → ρ+ ρ- in a sample of 89 million BB̄ pairs recorded with the BABAR detector. The number of observed events is 88-21 +23±9 with a significance of 5.1 standard deviations with systematic uncertainties included. The branching fraction and the longitudinal polarization are measured to be β(B0 → ρ+ ρ-) = (25-6-6 +7+5× 10-6 and ΓLΓ = 0.98-0.08 +0.02±0. 03, respectively.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics