Measurement of B⁰→D_s^(*)+D*^- branching fractions and B⁰→D_s*⁺D*^- polarization with a partial reconstruction technique

We present a study of the decays B⁰→D_s^*+D^*-, using 20.8 fb^-1 of e⁺e^- annihilation data recorded with the BABAR detector. The analysis is conducted with a partial reconstruction technique, in which only the D^(*)+ and the soft pion from the D^*- decay are reconstructed. We measure the branching fractions γ(B⁰ →D_s⁺D^*-)= (1.03±0.14±0.13±0.26)% and ß(B⁰→D_s ^*+D^*-)= (1.97±0.15±0.30±0.49)%, where the first error is statistical, the second is systematic, and the third is the error due to the D_s⁺→φπ⁺ branching fraction uncertainty. From the B⁰→D_s^*+D^*- angular distributions, we measure the fraction of longitudinal polarization Γ_L/Γ=(51.9±5.0±2.8)%, which is consistent with theoretical predictions based on factorization.