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

Abstract

We present improved measurements of the branching fraction B , the longitudinal polarization fraction f L , and the direct C P asymmetry A C P in the B meson decay channel B + → ρ + ρ 0 . The data sample was collected with the BABAR detector at SLAC. The results are B ( B + → ρ + ρ 0 ) = ( 23.7 ± 1.4 ± 1.4 ) × 10 − 6 , f L = 0.950 ± 0.015 ± 0.006 , and A C P = − 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 t d V ∗ t b / V u d V ∗ u b ) to be ( 92.4 + 6.0 − 6.5 ) ° .