Study of (B)over-bar0→D(*)0π+π- decays

We report on a study of (B) over bar (0) --> D((*)0)pi(+)pi(-) decays using 29.1 fb(-1) of e(+)e(-) annihilation data recorded at the gamma(4S) resonance with the Belle detector at the KEKB storage ring. Making no assumptions about the intermediate mechanism, the branching fractions for (B) over bar (0) --> D(0)pi(+)pi(-) and (B) over bar (0) --> D(*0)pi(+)pi(-) are determined to be (8.0 +/- 0.6 +/- 1.5) X 10(-4) and (6.2 +/- 1.2 +/- 1.8) x 10(-4), respectively. An analysis of (B) over bar (0) --> D(0)pi(+)pi(-) candidates yields to the first observation of the color-suppressed hadronic decay (B) over bar (0) --> D(0)rho(0) with the branching fraction (2.9 +/- 1.0 +/- 0.4) x 10(-4). We measure the ratio of branching fractions B((B) over bar (0) --> D(0)rho(0))/B((B) over bar (0) --> D(0)omega) = 1.6 +/- 0.8. (C) 2002 Elsevier Science B.V. All rights reserved.