Measurement of the branching fraction and CP asymmetry in B0→π0π0 decays, and an improved constraint on ϕ2

We measure the branching fraction and CP violation asymmetry in the decay B-0 -> pi(0)pi(0), using a data sample of 752 x 10(6) B (B) over bar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. The obtained branching fraction and direct CP asymmetry are B(B -> pi(0)pi(0)) = [1.31 +/- 0.19(stat) +/- 0.19(syst)] x 10(-6) and A(CP) = +0.14 +/- 0.36(stat) +/- 0.10(syst), respectively. The signal significance, including the systematic uncertainty, is 6.4 standard deviations. We combine these results with Belle's earlier measurements of B-0 -> pi(+)pi(-) and B-+/- -> pi(+/-)pi(0) to exclude the CP-violating parameter phi(2) from the range 15.5 degrees < phi(2) < 75.0 degrees at 95% confidence level.