Observation of B_s0->D_s*- pi+, B_s0->D_s(*)- rho+ Decays and Measurement of B_s0->D_s*- rho+ Polarization

First observations of the B_s0->D_s*- pi+, B_s0->D_s- rho+ and B_s0->D_s*- rho+ decays are reported together with measurements of their branching fractions: B(B_s0->D_s*- pi+)=(2.4 +0.5-0.4(stat.) ±0.3(syst.) ±0.4(fs))x10^(-3), B(Bs->D_s- rho+)=(8.5 +1.3-1.2(stat.) ±1.1(syst.) ±1.3(fs))x10^(-3) and B(Bs->D_s*- rho+)=(11.8 +2.2-2.0(stat.) ±1.7(syst.) ±1.8(fs))x10^(-3) (f_s=N(B_s()B_s()-bar)/N(b b-bar)). From helicity-angle distributions, we measured the longitudinal polarization fraction in B_s0->D_s*- rho+ decays to be f_L(Bs->D_s*- rho+)=1.05 +0.08-0.10(stat.) +0.03-0.04(syst.). These results are based on a 23.6 /fb data sample collected at the Y(5S) resonance with the Belle detector at the KEKB e+e- collider.