Branching fraction measurement of B0 --> D(*)- pi+, B- --> D(*)0 pi- and isospin analysis of B --> D(*) pi decays

Abstract

Using 65 million ${\rm Y}(4S)\to B\bar{B}$ 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 $\mathcal{B}(\overline{B^0}\to D^{+}{\pi }^{-})=(2.55\pm 0.05\pm 0.16)\times 10^{-3}$, $\mathcal{B}(\overline{B^0}\to D^{\ast +}{\pi }^{-})=(2.79\pm 0.08\pm 0.17)\times 10^{-3}$, $\mathcal{B}(B^{-}\to D^0{\pi }^{-})=(4.90\pm 0.07\pm 0.22)\times 10^{-3}$ and $\mathcal{B}(B^{-}\to D^{\ast 0}{\pi }^{-})=(5.52\pm 0.17\pm 0.42)\times 10^{-3}$, 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 $\overline{B^0}\to D^{(\ast )0}{\pi }^0$, the cosines of the strong phase difference $\delta$ between the $I=1/2$ and $I=3/2$ isospin amplitudes are determined to be $\cos \delta =0.872_{-0.007-0.029}^{+0.008+0.031}$ for the $\bar{B}\to D\pi$ process and $\cos \delta =0.924_{-0.017-0.054}^{+0.019+0.063}$ for the $\bar{B}\to D^{\ast }\pi$ process. Under the isospin symmetry, the results for $\cos \delta$ suggest that final-state interactions are present in the $D\pi$ system.

8 pages, 3 postscript figues, submitted to Phys. Rev. D