Family Non-universal Z′ effects on Bq-Bq mixing, B→ Xₛ μ+μ- and Bₛ→ μ+μ- Decays

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Motivated by the large discrepancy of CP-violating phase in Bₛ-Bₛ mixing between the experimental data and the Standard Model prediction, we pursue possible solutions within a family non-universal Z′ model. Within such a specific model, we find that both the Bₛ-Bₛ mixing anomaly and the well-known "πK puzzle" could be moderated simultaneously with a nontrivial new weak phase, ϕˡₛ -72∘ (S1) or -82∘ (S2). With the stringently constrained Z′ coupling Bsbˡ, we then study the Z′ effects on the rare B→ Xₛ μ+μ- and Bₛ→ μ+μ- decays, which are also induced by the same b→ s transition. The observables of B→ Xₛ μ+μ-, at both high and low q² regions, are found to be able to put strong constraints on the μ-μ-Z′ coupling, Bμμˡ,ʳ 10⁻². It is also shown that the combined constraints from Bₛ-Bₛ mixing, B→ πK and B→ Xₛ μ+μ- do not allow a large Z′ contribution to the pure leptonic Bₛ→μ+μ- decay.