Improved Measurement of the Cabibbo-Kobayashi-Maskawa Angle α Using B0(¯¯¯B)→ρ+ρ− Decays

Abstract

We present results from an analysis of B 0 ( ¯¯¯ B 0 ) → ρ + ρ − using 232 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction f L = 0.978 ± 0.014 ( stat ) + 0.021 − 0.029 ( syst ) and the C P -violating parameters S L = − 0.33 ± 0.24 ( stat ) + 0.08 − 0.14 ( syst ) and C L = − 0.03 ± 0.18 ( stat ) ± 0.09 ( syst ) . Using an isospin analysis of B → ρ ρ decays, we determine the unitarity triangle parameter α . The solution compatible with the standard model is α = ( 100 ± 13 ) ° .