Direct Mass Limits for Chiral Fourth-Generation Quarks in All Mixing Scenarios

Present limits on chiral fourth-generation quark masses $m_{b^{\mathrm{\prime }}}$ and $m_{t^{\mathrm{\prime }}}$ are broadly generalized and strengthened by combining both $t^{\mathrm{\prime }}$ and $b^{\mathrm{\prime }}$ decays and considering the full range of $t^{\mathrm{\prime }}$ and $b^{\mathrm{\prime }}$ flavor-mixing scenarios (with the lighter generations). Various characteristic mass-splitting choices are considered. With $m_{t^{\mathrm{\prime }}}>m_{b^{\mathrm{\prime }}}$ we find that CDF limits on the $b^{\mathrm{\prime }}$ mass vary by no more than 10-20% with any choice of flavor-mixing, while for the $t^{\mathrm{\prime }}$ mass, we typically find stronger bounds, in some cases up to $m_{t’} > 430$GeV\mathrm{.}For$m_{b’} > m_{t’}$wefind$m_{b’} > 380 - 430$ GeV, depending on the flavor-mixing and the size of the $m_{t^{\mathrm{\prime }}}-m_{b^{\mathrm{\prime }}}$ mass splitting.