Improved Measurement of B+→ρ+ρ0 and Determination of the Quark-Mixing Phase Angle α

We present improved measurements of the branching fraction B, the longitudinal polarization fraction fL, and the direct CP asymmetry ACP in the B meson decay channel B+→ρ+ρ0. The data sample was collected with the BABAR detector at SLAC. The results are B(B+→ρ+ρ0)=(23.7±1.4±1.4)×10-6, fL=0.950±0.015±0.006, and ACP=-0.054±0.055±0.010, where the uncertainties are statistical and systematic, respectively. Based on these results, we perform an isospin analysis and determine the Cabibbo-Kobayashi-Maskawa phase angle α=arg(-VtdVtb*/VudVub*) to be (92.4-6.5+6.0)°.