Z-mediated charge and CP asymmetries and FCNCs in $B_{d,s}$ processes

We show model-independently that the negative like-sign charge asymmetry $(-A_{s\mathrm{\ell }}^b)$ is less than $3.16\times {10}^{-3}$ when the constraints from the $B_q-{\bar{B}}_q$ mixings and the time-dependent CP asymmetries (CPAs) for $B_q\to J\mathrm{/}\mathrm{\Psi }{M}_q$ with $M_q=K,\varphi$ and $q=d,s$ are taken into account. Although the result is smaller than the measured value by the D{\O} Collaboration at Fermilab, there is still plenty of room to have new physics, which is sensitive to new CP violating effects, as the standard model (SM) prediction is $(2.3_{-0.5}^{+0.6})\times {10}^{-4}$. To illustrate the potential large $\mathrm{\mid }{A}_{s\mathrm{\ell }}^b\mathrm{\mid }$, we show the influence of new $SU(2{)}_L$ singlet exotic quarks in the vector-like quark model, where the $Z$-mediated flavor changing neutral currents (FCNCs) are generated at tree level. In particular, we demonstrate that (a) the like-sign charge asymmetry could be enhanced by a factor of two in magnitude; (b) the CPA of $\sin 2{\beta }_s^{J\mathrm{/}\mathrm{\Psi }\varphi }$ could reach to $-15$; © the CPA of $\sin 2{\beta }_{\varphi K_S}$ could be higher than $\sin 2{\beta }_{J\mathrm{/}\mathrm{\Psi }{K}_S}$ when $\mathrm{\mid }{A}_{s\mathrm{\ell }}^b\mathrm{\mid }$ is larger than the SM prediction; and (d) the branching ratio for $B_s\to {\mu }^{+}{\mu }^{-}$ could be as large as $0.6\times {10}^{-8}$.