Measurement of the branching fractions of B¯ → D()K−KS∗0 and B¯ → D()Ds− decays at Belle II

We present measurements of the branching fractions of eight B ¯ 0 → D (*)+ K − K S ∗ 0 , B − → D (*)0 K − K S ∗ 0 decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4 S ) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb − 1 . The event yields are extracted from fits to the distributions of the difference between expected and observed B meson energy, and are efficiency-corrected as a function of m ( K − K S ∗ 0 ) and m ( D (*) K S ∗ 0 ) in order to avoid dependence on the decay model. These results include the first observation of B ¯ 0 → D + K − K S 0 , B − → D* 0 K − K S 0 , and B ¯ 0 → D* + K − K S 0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of the K − K S ∗ 0 systems are compatible with quasi-two-body decays via a resonant transition with spin-parity J P = 1 − for the K − K S 0 systems and J P = 1 + for the K − K* 0 systems. We also present measurements of the branching fractions of four B ¯ 0 → D (*)+ D s − , B − → D (*)0 D s − decay channels with a precision compatible to the current world averages.