We study the effects of the fourth quark generation model in ■_s →π-K+decay.Combining with the up-to-date experimental measurement for B(■_s →π-K +) and A dir cp(■_s →π-K +) by the CDF Collaboration,we derive the new bound of weak phase φ bd,which are 0 < φ bd < 44,321 < φ bd < 360 and 0 < φ bd < 26,342 < φ bd < 360 for m t = 400 and 600 GeV respectively.In these regions,B(■_s →π-K +) and A dir cp(■_s →π-K +) consist with the current experimental data within errors.
In this paper, we calculate the branching ratios of Λb→pK-and p∏- decays in the flavor changing Z' model. We find that the branching ratios for these two decay modes are sensitive to the contributions of the Z' boson. For Λb→pK decay, if the left-handed couplings are equal to the right-handed couplings, the branching ratio of this decay could match up to the currently experimental data for ξs =0.01 and -52° <φsL<132°, or ξs =0.004 and 0°<φsL<84; if only the left-handed couplings are considered, it could match up to the experimental data for ξs =0.01 and 10<φsL<138. And for Λb→p∏- decay, if the left-handed and right-handed couplings are equal, the branching ratio of Λb→p∏- decay may be consistent with the currently experimental data with ξd =0.05 and -135<φdL<43°, if only the left-handed couplings are considered, it may be consistent with ξd =0.05 and -114<φsL<8°.
