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 − → D K − and B − → D ∗ K − followed by D → K + π − , where D ( * ) indicates a D ( * ) 0 or a ¯¯¯ D ( * ) 0 meson, and D ∗ → D π 0 or D ∗ → D γ . These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity triangle angle γ due to interference between the b → c transition B − → D ( * ) 0 K − followed by the doubly Cabibbo-suppressed decay D 0 → K + π − , and the b → u transition B − → ¯¯¯ D ( * ) 0 K − followed by the Cabibbo-favored decay ¯¯¯ D 0 → K + π − . We also report an analysis of the decay B − → D ( * ) π − with the D decaying into the doubly Cabibbo-suppressed mode D → K + π − . Our results are based on 467 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at SLAC. We measure the ratios R ( * ) of the suppressed ( [ K + π − ] D K − / π − ) to favored ( [ K − π + ] D K − / π − ) branching fractions as well as the C P asymmetries A ( * ) of those modes. We see indications of signals for the B − → D K − and B − → D ∗ D π 0 K − suppressed modes, with statistical significances of 2.1 and 2.2 σ , respectively, and we measure: R D K = ( 1.1 ± 0.6 ± 0.2 ) × 10 − 2 , A D K = − 0.86 ± 0.47 + 0.12 − 0.16 , R ∗ ( D π 0 ) K = ( 1.8 ± 0.9 ± 0.4 ) × 10 − 2 , A ∗ ( D π 0 ) K = + 0.77 ± 0.35 ± 0.12 , R ∗ ( D γ ) K = ( 1.3 ± 1.4 ± 0.8 ) × 10 − 2 , A ∗ ( D γ ) K = + 0.36 ± 0.94 + 0.25 − 0.41 , where the first uncertainty is statistical and the second is systematic. We use a frequentist approach to obtain the magnitude of the ratio r B ≡ | A ( B − → ¯¯¯ D 0 K − ) / A ( B − → D 0 K − ) | = ( 9.5 + 5.1 − 4.1 ) % , with r B < 16.7 % at 90% confidence level. In the case of B − → D ∗ K − we find r ∗ B ≡ | A ( B − → ¯¯¯ D * 0 K − ) / A ( B − → D * 0 K − ) | = ( 9.6 + 3.5 − 5.1 ) % , with r ∗ B < 15.0 % at 90% confidence level.