Double-Lepton Polarization Asymmetries in $B_s \rar \phi \ell^+ \ell^-$   Decay in the Fourth-Generation Standard Model
  In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the $B_s \rar \phi \ell^+ \ell^-$ decay. It is shown that these asymmetries in $B_s \rar \phi \ell^+ \ell^-$ decay compared with those of $B \rar K \ell^+ \ell^-$ decay are more sensitive to the fourth-generation parameters. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the $B_s \rar \phi \ell^+ \ell^-$ decay. 
S. M. Zebarjad, F. Falahati and H. Mehranfar