Study of B-0 -> rho(0)rho(0) decays, implications for the CKM angle phi(2) and search for other B-0 decay modes with a four-pion final state

We present a study of the branching fraction of the decay B-0 -> rho(0)rho(0) and the fraction of longitudinally polarized rho(0) mesons in this decay. The results are obtained from the final data sample containing 772 x 10(6) B (B) over bar pairs collected at the gamma(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We find 166 +/- 59 B-0 -> rho(0)rho(0) events (including systematic uncertainties), corresponding to a branching fraction of B(B-0 -> rho(0)rho(0)) = (1.02 +/- 0.30(stat) +/- 0.15(syst)) x 10(-6) with a significance of 3.4 standard deviations and a longitudinal polarization fraction f(L) = 0.21(-0.22)(+0.18()stat) +/- 0.15(syst). We use the longitudinal polarization fraction to determine the Cabibbo-Kobayashi-Maskawa matrix angle phi(2) = (84.9 +/- 13.5)degrees through an isospin analysis in the B ->rho rho system. We furthermore find 125 +/- 41 B-0 -> f(0)rho(0) events, corresponding to B(B-0 -> f(0)rho(0)) x B(f(0) -> pi(+)pi(-)) = (0.78 +/- 0.22(stat) +/- 0.11(syst)) x 10(-6), with a significance of 3.1 standard deviations. We find no other significant contribution with the same final state, and set upper limits at 90% confidence level on the (product) branching fractions, B(B-0 -> pi(+)pi(-)pi(+)pi(-)) < 11.2 x 10(-6), B(B-0 -> rho(0)pi(+)pi(-)) < 12.0 x 10(-6), B(B-0 -> f(0)pi(+)pi(-)) x B(f(0) -> pi(+)pi(-)) < 3.0 x 10(-6) and B(B-0 -> f(0)f(0)) x B(f(0) -> pi(+)pi(-))(2) < 0.2 x 10(-6).