Study of B0 → ρ+ρ− decays and constraints on the CKM angle α

Abstract

We present results from an analysis of B 0 → ρ + ρ − decays using ( 383.6 ± 4.2 ) × 10 6 B ¯¯¯ B pairs collected by the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The measurements of the B 0 → ρ + ρ − branching fraction, longitudinal polarization fraction f L , and the C P -violating parameters S long and C long are as follows: B ( B 0 → ρ + ρ − ) = ( 25.5 ± 2.1 ( stat ) + 3.6 − 3.9 ( syst ) ) × 10 − 6 , f L = 0.992 ± 0.024 ( stat ) + 0.026 − 0.013 ( syst ) , S long = − 0.17 ± 0.20 ( stat ) + 0.05 − 0.06 ( syst ) , C long = 0.01 ± 0.15 ( stat ) ± 0.06 ( syst ) . We determine the unitarity triangle angle α , using an isospin analysis of B → ρ ρ decays. One of the two solutions, α = [ 73.1 , 117.0 ] ° at 68% confidence level, is compatible with standard model-based fits of existing data. Constraints on the unitarity triangle are also evaluated using an S U ( 3 ) symmetry-based approach.