Improved measurement of the Cabibbo-Kobayashi-Maskawa angle α using B0(B̄)→ρ+ρ- decays

Abstract

We present results from an analysis of B0(B̄0)→ρ+ρ- using 232×106 Υ(4S)→BB̄ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction fL=0.978±0.014(stat)+0.021-0.029(syst) and the CP-violating parameters SL=-0.33±0.24(stat)+0.08-0.14(syst) and CL=-0.03±0.18(stat)±0.09(syst). Using an isospin analysis of B→ρρ decays, we determine the unitarity triangle parameter α. The solution compatible with the standard model is α=(100±13) °. © 2005 The American Physical Society.