Measurement of the branching fraction, polarization, and CP asymmetries in B0→ρ0ρ0 decay, and implications for the CKM angle α

We study B 0 → ρ 0 ρ 0 decays in a sample of 465 × 10 6 Υ ( 4 S ) → B ¯¯¯ B events collected with the BABAR detector at the PEP-II asymmetric-energy e + e − collider located at the Stanford Linear Accelerator Center (SLAC). We measure the branching fraction B = ( 0.92 ± 0.32 ± 0.14 ) × 10 − 6 and longitudinal polarization fraction f L = 0.75 + 0.11 − 0.14 ± 0.05 , where the first uncertainty is statistical and the second is systematic. The evidence for the B 0 → ρ 0 ρ 0 signal has a significance of 3.1 standard deviations, including systematic uncertainties. We investigate the proper-time dependence of the longitudinal component in the decay and measure the C P -violating coefficients S 00 L = ( 0.3 ± 0.7 ± 0.2 ) and C 00 L = ( 0.2 ± 0.8 ± 0.3 ) . We study the implication of these results for the unitarity triangle angle α