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^(*)0K⁻K_S^∗0 decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4S) 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_S⁰, B⁻ → D*⁰K⁻K_S⁰, and B¯⁰ → D*⁺K⁻K_S⁰ 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_S⁰ 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^(*)0D_s⁻ decay channels with a precision compatible to the current world averages.