B→s decays in a model with Z-mediated flavor changing neutral current

In the scenario with Z-mediated flavor changing neutral current occurring at the tree level due to the addition of a vectorlike isosinglet down-type quark d′ to the SM particle spectrum, we perform a χ2 fit using the flavor physics data and obtain the best fit value along with errors of the tree level Zb̄s coupling, Usb. The fit indicates that the new physics coupling is constrained to be small: we obtain |Usb|≤3. 40×10-4 at 3σ. Still, this does allow for the possibility of new physics signals in some of the observables, such as semileptonic CP asymmetry in Bs decays. © 2012 American Physical Society.