Observation of Bs0→Ds*-π+ and Bs0→Ds(*)-ρ+ and Measurement of the Bs0→Ds*-ρ+ Longitudinal Polarization Fraction

First observations of the Bs0→Ds*-π+, Bs0→Ds-ρ+ and Bs0→Ds*-ρ+ decays are reported together with measurements of their branching fractions: B(Bs0→Ds*-π+)=[2.4-0.4+0.5(stat)±0.3(syst)± 0.4(fs)]x10-3, B(Bs0→Ds-ρ+)=[8.5-1.2+1.3(stat)±1.1(syst)±1.3(fs)]x10-3 and B(Bs0→Ds*-ρ+)=[11.9-2.0+2.2(stat)±1.7(syst)±1.8(fs)]x10-3 (fs=NBs(*)Bs(*)/Nbb). From helicity-angle distributions, we measured the longitudinal polarization fraction in Bs0→Ds*-ρ+ decays to be fL(Bs0→Ds*-ρ+)=1.05-0.10+0.08(stat)-0.04+0.03(syst). These results are based on a 23.6 fb-1 data sample collected at the Υ(5S) resonance with the Belle detector at the KEKB e+e- collider.