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^b _sℓ) is less than 3.16 × 10^-3 when the constraints from the B_q - B̄_q mixings and the time-dependent CP asymmetries (CPAs) for B_q → J/ψ_q with M_q = K, φ and q = d, s are taken into account. Although the result is smaller than the measured value by the DØ 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)× 10^-4. To illustrate the potential large |Ab _sℓ|, 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 2β_sJ/ψφ could reach to -15%; (c) the CPA of sin 2β_φKS could be higher than sin 2β _ψJ/KS when |A_sℓ^b