Search for b → u transitions in B^± → [K^∓π^±π^0]_DK^± decays

Abstract

We present a study of the decays B^±→DK^± with D mesons reconstructed in the K^+π^-π^0 or K^-π^+π^0 final states, where D indicates a D^0 or a D̅^0 meson. Using a sample of 474×10^6 BB̅ 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^±π^0]_DK^±)/Γ(B^±→[K^±π^∓π^0]_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 r_B of the magnitudes of the b→u and b→c amplitudes r_B<0.13 at 90% probability.

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