Branching fraction measurement of B̅ 0→D(*)+π- and B-→D(*)0π- and isospin analysis of B̅ →D(*)π decays

Using 65×10^6 Υ(4S)→BB̅ events collected with the BABAR detector at the PEP-II e+e- storage ring at the Stanford Linear Accelerator Center, we measure the color-favored branching fractions B(B̅ 0→D+π-)=(2.55±0.05±0.16)×10-3, B(B̅ 0→D*+π-)=(2.79±0.08±0.17)×10-3, B(B-→D0π-)=(4.90±0.07±0.22)×10-3 and B(B-→D*0π-)=(5.52±0.17±0.42)×10-3, where the first error is statistical and the second is systematic. With these results and the current world average for the branching fraction for the color-suppressed decay B̅ 0→D(*)0π0, the cosines of the strong phase difference δ between the I=1/2 and I=3/2 isospin amplitudes are determined to be cos⁡δ=0.872-0.007-0.029+0.008+0.031 for the B̅ →Dπ process and cos⁡δ=0.924-0.017-0.054+0.019+0.063 for the B̅ →D*π process. Under the isospin symmetry, the results for cos⁡δ suggest the presence of final-state interactions in the Dπ system.