Z-mediated charge and CP asymmetries and FCNCs in $B_{d,s}$ processes. (arXiv:1006.5216v1 [hep-ph])

We show model-independently that the upper bound for the negative like-sign
charge asymmetry $(-A^b_{s\ell})$ is $ (3.16_{-0.48}^{+0.49})\times 10^{-3}$
when the constraints from the $B_q-\bar B_q$ mixings and the time-dependent CP
asymmetries (CPAs) for $B_q\to J/\Psi M_q$ with $M_q=K,\phi$ and $q=d,s$ are
taken into account. Although the upper bound is smaller than the measured value
by the D{\O} Collaboration at Fermilab, it is still one order of magnitude
larger than the standard model (SM) prediction and sensitive to new CP
violating effects. To illustrate the potential large $|A^{b}_{s\ell}|$, 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 $\sin2\beta^{J/\Psi \phi}_s$ could reach to $-15\%$; (c) the CPA of
$\sin2\beta_{\phi K_S}$ could be higher than $\sin2\beta_{J/\Psi K_S}$ when
$|A^b_{s\ell}|$ is larger than the SM prediction; and (d) the branching ratio
for $B_s\to \mu^+ \mu^-$ could be as large as .6\times 10^{-8}$.

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