Study of B_s →ϕ (ρ^0, ω) Decays in Standard Model and Family Non-universal Z^' Model

Within QCD factorization approach, we employ the new results of form factors of B_s →ϕ and calculate the branching fractions, CP asymmetries (CPAs) and polarization fractions of the decay modes B_s →ϕ (ρ^0, ω) in both the standard model (SM) and the family non-universal Z^' model. We find that in SM the above observables are relate to two parameters ρ_H and ϕ_H, which characterize the end-point divergence in the hard spectator-scattering amplitudes. When setting ρ_H=0.5 and ϕ_H∈ [-180,180]^∘, the theoretical uncertainties are large. By combining the experimental data, our results can be used to constrain these two parameters. Supposing ρ_H=0, we study the effects of Z^' boson on the concerned observables. With the available branching fraction of B_s →ϕρ^0, the possible ranges of parameter spaces are obtained. Within the allowed parameter spaces, the branching fraction of B_s →ϕω can be enlarged remarkably. Furthermore, the new introduced weak phase plays important roles in significantly affecting the CPAs and polarization fractions, which are important observables for probing the effects of NP. If these decay modes were measured in the on-going LHC-b and Belle-II experiments in future, the peculiar deviation from SM could provide a signal of the family non-universal Z^' model, which can also be used to constrain the mass of Z^' boson in turn.