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 f_L, and the direct CP asymmetry A_(CP) in the B meson decay channel B^+ → p^+p^0. The data sample was collected with the BABAR detector at SLAC. The results are B(B^+ → p^+p^0)=(23.7±1.4±1.4)×10^(-6), f_L=0.950±0.015±0.006, and A_(CP)=-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(-V_(td)V^*_(tb)/V_(ud)V*ub) to be (92.4^(+6.0)_(-6.5))°.