Study of B0 → ρ+ ρ- Decays and implications for the CKM angle φ 2

Abstract

We present a measurement of the branching fraction and the longitudinal polarization fraction of B0→ρ+ρ- decays, as well as the time-dependent CP violating parameters in decays into longitudinally polarized ρ+ρ- pairs with Belle's final data set of 772×106 BB¯ pairs, at the (4S) resonance, collected at the asymmetric-energy e+e- collider KEKB. We obtain B(B0→ρ+ρ-)=(28.3±1.5(stat)±1.5(syst))×10-6, fL=0.988±0.012(stat)±0.023(syst), ACP=0.00±0.10(stat)±0.06(syst), SCP=-0.13±0.15(stat)±0.05(syst). We perform an isospin analysis to constrain the Cabibbo-Kobayashi-Maskawa angle φ2 and obtain two solutions with φ2=(93.7±10.6)°, being most compatible with other Standard-Model based fits to the data.