Fourth generation effects in processes induced by the $b \rightarrow s$ transition

Abstract. We study the effects of sequential fourth quark generation in rare $B \rightarrow K(K^*) \ell^+ \ell^-$ decays induced by the $b \rightarrow s$ transition and in Bs0-$ \bar{B}_s^0$ mixing. Using the experimental values on the branching ratios of the $B \rightarrow X_s \gamma$ and $B \rightarrow K(K^*) \ell^+ \ell^-$ decays, the allowed regions for $\left\vert V_{tb} V_{ts}^*\right\vert$ and $\left\vert V_{t^{'} b} V_{t^{'} s}^*\right\vert$ are determined as a function of the t' quark mass.