Predictions for $$B_s \rightarrow {\bar{K}}^* \ell \,\ell $$ in non-universal $$Z'$$ models

Abstract

AbstractThe lepton flavor universality violating (LFUV) measurements $$R_K$$RK and $$R_{K^*}$$RK∗ in B meson decays can be accounted for in non-universal $$Z'$$Z′ models. We constrain the couplings of these $$Z'$$Z′ models by performing a global fit to correlated $$b \rightarrow s \ell \ell $$b→sℓℓ and $$b \rightarrow d \ell \ell $$b→dℓℓ processes, and calculate their possible implications for $$B_s \rightarrow {\bar{K}}^*\ell \ell $$Bs→K¯∗ℓℓ observables. For real new physics (NP) couplings, the 1$$\sigma $$σ favored parameters allow the corresponding LFUV ratio $$R_{K^*}^{(s)}$$RK∗(s) in $$B_s \rightarrow {\bar{K}}^*\ell \ell $$Bs→K¯∗ℓℓ to range between 0.8 and 1.2 at low $$q^2$$q2. Complex NP couplings improve the best fit only marginally, however they allow a significant enhancement of the branching ratio, while increasing the range of $$R_{K^*}^{(s)}\ $$RK∗(s)at low $$q^2$$q2 to 0.8–1.8. We find that NP could cause zero-crossing in the forward–backward asymmetry $$A_{FB}$$AFB to shift towards lower $$q^2$$q2 values, and enhancement in the magnitude of integrated $$A_{FB}$$AFB. The CP asymmetry $$A_{CP}$$ACP may be suppressed and even change sign. The simultaneous measurements of integrated $$R_{K^*}^{(s)}\ $$RK∗(s)and $$A_{CP}$$ACP values to 0.1 and 1% respectively, would help in constraining the effective NP Wilson coefficient $$C_9$$C9 in $$ b \rightarrow d \mu \mu $$b→dμμ interactions.