Effects of a Family Non-universal Z' Boson in B-bard → μ+μ- and B- → π-μ+μ-, ρ-μ+μ- Decays

Motivated by the recently updated experimental measurement on B-bard → μ+μ- and B- → π-μ+μ- decays by CDF and Belle collaborations, we revisit these decays, as well as B- → ρ-μ+μ- decay, within the Standard Model, and evaluate the effects of a family non-universal Z' boson. Under the constraint from B(B- → π-μ+μ-), we find the ranges of the Z' couplings SLRμμ < -5.2 × 10-2 or DLRμμ < -8.1 × 10-2 are excluded. Within the allowed Z' parameters spaces, comparing with the SM predictions, we find that B( B-bar d → μ+μ-), B(B- → π-μ+μ-), and B(B- → ρ-μ+μ-) could be enhanced by a factor about 226%, 245%, and 254%, respectively, by Z' contributions. However, they are hardly to be reduced. Furthermore, the zero crossing in the normalized forward-backward asymmetry spectrum of B- → ρ-μ+μ- decay at low dimuon mass always exists. (physics of elementary particles and fields)