Fourth generation effects in rare $B_s \rightarrow \ell^+ \ell^-$ and $B_s \rightarrow \ell{l}^+ \ell{l}^- \gamma$ decays

Abstract.

The contribution of the fourth generation quarks to the rare $B_s \rightarrow \ell^+ \ell^-$ and $B_s \rightarrow \ell^+ \ell^- \gamma$ decays are studied. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix elements |V _tb V _ts ^*| and $\vert V_{t^\prime b} V_{t^\prime s}^* \vert$ are obtained from the existing experimental result for the branching ratio of the $B \rightarrow X_s \gamma$ decay. The branching ratios of the above-mentioned decays, as well as the photon spectrum in the $B_s \rightarrow \ell^+ \ell^- \gamma$ decay, are studied. It is found that the results are sensitive to the existence of the fourth generation.