Study of ¯ B 0 → D ( ∗ )0 π + π − Decays

We report on a study of ¯ B 0 → D ( ∗ )0 π + π − decays using 29.1 fb − 1 of e + e − an-nihilation data recorded at the Υ(4 S ) resonance with the Belle detector at the KEKB storage ring. Making no assumptions about the intermediate mechanism, the branching fractions for ¯ B 0 → D 0 π + π − and ¯ B 0 → D ∗ 0 π + π − are determined to be (8 . 0 ± 0 . 6 ± 1 . 5) × 10 − 4 and (6 . 2 ± 1 . 2 ± 1 . 8) × 10 − 4 respectively. An analysis of ¯ B 0 → D 0 π + π − candidates yields to the first observation of the color-suppressed hadronic decay ¯ B 0 → D 0 ρ 0 with the branching fraction (2 . 9 ± 1 . 0 ± 0 . 4) × 10 − 4 . We measure the ratio of branching fractions B ( ¯ B 0 → D 0 ρ 0 )/ B ( ¯ B 0 → D 0 ω ) = 1.6 ± 0.8.