Estimating r(B)(D pi) as an input to the determination of the CKM angle gamma

The interference between Cabibbo-favored and Cabibbo-suppressed B -> D pi decay amplitudes provides sensitivity to the CKM angle gamma. The relative size of the interfering amplitudes is an important ingredient in the determination of gamma. Using branching fractions from various B -> Dh decays, and the measured value for r(B)(DK) the magnitude of the amplitude ratio of B+ -> D-0 pi(+) and B+ -> D-0 pi(+) decays is estimated to be r(B)(D pi) = 0.0053 +/- 0.0007.