UC Berkeley

We present a study of the decays B±→DK ± with D mesons reconstructed in the K+π -π0 or K-π+π0 final states, where D indicates a D0 or a D̄0 meson. Using a sample of 474×106 BB̄ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we measure the ratios R ±Γ(B±→[K±π ±π0]DK±)Γ(B ±→[K±π±π0] DK±). We obtain R+=(5-10+12(stat)- 4+2(syst))×10-3 and R-=(12-10+12(stat)-5+3(syst)) ×10-3, from which we extract the upper limits at 90% probability: R+<23×10-3 and R -<29×10-3. Using these measurements, we obtain an upper limit for the ratio rB of the magnitudes of the b→u and b→c amplitudes rB<0.13 at 90% probability. © 2011 American Physical Society.