Measurement of the branching fractions of $$ \overline{B} $$ → D(*)K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ and $$ \overline{B} $$ → D(*)$$ {D}_s^{-} $$ decays at Belle II

We present measurements of the branching fractions of eight B¯0 → D(*)+K−KS∗0, B− → D(*)0K−KS∗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−KS∗0) and m(D(*)KS∗0) in order to avoid dependence on the decay model. These results include the first observation of B¯0 → D+K−KS0, B− → D*0K−KS0, and B¯0 → D*+K−KS0 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−KS∗0 systems are compatible with quasi-two-body decays via a resonant transition with spin-parity JP = 1− for the K−KS0 systems and JP = 1+ for the K−K*0 systems. We also present measurements of the branching fractions of four B¯0 → D(*)+Ds−, B− → D(*)0Ds− decay channels with a precision compatible to the current world averages.