Constraining Fourth Generation with $Bto X_s gamma$

Using the theoretical and experimental results on $B to X_s gamma$, a four-generation SM is analyzed to constrain the combination of the $4times 4$ Cabibbo-Kobayashi-Maskawa factor $V_{t^prime s}^* V_{t^prime b}$ as a function of the $t^prime$--quark mass. It is observed that the results for the above--mentioned physical quantities are essentially different from the previous predictions for certain solutions of the CKM factor. Influences of the new model is used to predict CP violation in $B to X_s gamma$ decay at the order of $A_{CP}=5%$, stemming from the appearance of complex phases of $V_{t^prime s}^* V_{t^prime b}$ and of Wilson coefficients $C_7$, $C_8$, in the related process. The above mentioned physical quantities can serve as efficient tools in search of the fourth generation.