Measurement of the branching fraction, polarization, and CP asymmetry in B0 -> rho+rho- decays

We have measured the branching fraction, longitudinal polarization fraction f_L, and the CP asymmetry coefficients A and S in B0 -> rho+rho- decays. These results are obtained from a 253 fb-1 data sample containing 275 million B\bar{B} pairs collected by the Belle detector running at the KEKB e+e- collider. We obtain B = [24.4 \pm 2.2 (stat) +3.8 -4.1 (syst)] x 10-6, f_L = 0.951 +0.033 -0.039 (stat) +0.029 -0.031 (syst), A = 0.00 \pm 0.30 (stat) +0.10 -0.09 (syst), and S = 0.09 \pm 0.42 (stat) \pm 0.08 (syst). These values are used to determine the CKM phase angle phi_2 (alpha) via an isospin analysis; the central value and one sigma error are (87 \pm 17) degrees, and 59 degrees < phi_2 < 115 degrees at 90% CL.