Search for b-->u transitions in B--->DK- and D*K- decays

Abstract

We report results from an updated study of the suppressed decays B--->DK- and B--->D*K- followed by D-->K+pi-, where D(*) indicates a D(*)0 or a D[over-bar] (*)0 meson, and D*-->Dpi0 or D*-->Dgamma. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity triangle angle gamma due to interference between the b-->c transition B--->D(*)0K- followed by the doubly Cabibbo-suppressed decay D0-->K+pi-, and the b-->u transition B--->D[over-bar] (*)0K- followed by the Cabibbo-favored decay D[over-bar] 0-->K+pi-. We also report an analysis of the decay B--->D(*)pi- with the D decaying into the doubly Cabibbo-suppressed mode D-->K+pi-. Our results are based on 467× 106 Υ(4S)-->BB[over-bar] decays collected with the BABAR detector at SLAC. We measure the ratios R(*) of the suppressed ([K+pi-]DK-/pi-) to favored ([K-pi+]DK-/pi-) branching fractions as well as the CP asymmetries A(*) of those modes. We see indications of signals for the B--->DK- and B--->DDpi0*K- suppressed modes, with statistical significances of 2.1 and 2.2σ, respectively, and we measure: RDK=(1.1±0.6±0.2)×10-2, ADK=-0.86±0.47-0.16+0.12, R(Dpi0)K*=(1.8±0.9± 0.4)×10-2, A(Dpi0)K*=+0.77±0.35±0.12, R(Dgamma)K*=(1.3±1.4±0.8)×10-2,A(Dgamma)K*=+0.36 ±0.94-0.41+0.25, where the first uncertainty is statistical and the second is systematic. We use a frequentist approach to obtain the magnitude of the ratio rB≡|A(B--->D[over-bar] 0K-)/A(B--->D0K-)|=(9.5-4.1+5.1)%, with rB<16.7% at 90% confidence level. In the case of B--->D*K- we find rB*≡|A(B--->D[over-bar] *0K-)/A(B--->D*0K-)|=(9.6-5.1+3.5)%, with rB*<15.0% at 90% confidence level.