Evidence for \u3ci\u3eB\u3c/i\u3e\u3csup\u3e0\u3c/sup\u3e → ρ\u3csup\u3e0\u3c/sup\u3e ρ\u3csup\u3e0\u3c/sup\u3e Decays and Implications for the Cabibbo-Kobayashi-Maskawa Angle α

Abstract

We search for the decays B0 → ρ0 ρ0, B0 → ρ0f0(980), and B0 → f0(980)f0(980) in a sample of about 384 × 106 Υ (4S)→ BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy ℯ+ ℯ- collider at Stanford Linear Accelerator Center. We find evidence for B0 → ρ0 ρ0 with 3.5σ significance and measure the branching fraction Ɓ = 1.07 ± 0:33 ± 0:19) × 10-6 and longitudinal polarization fraction fL = 0.87 ± 0.13 ± 0.04, where the first uncertainty is statistical, and the second is systematic. The uncertainty on the Cabibbo-Kobayashi-Maskawa quark-mixing matrix unitarity angle α due to penguin contributions in B→ ρρ decays is 18° at the 1σ level. We also set upper limits on the B0 → ρ0f0(980) and i\u3eB0 → f0(980)f0(980) decay rates