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

Abstract

Present limits on chiral fourth-generation quark masses $m_{b^{\prime }}$ and $m_{t^{\prime }}$ are broadly generalized and strengthened by combining both $t^{\prime }$ and $b^{\prime }$ decays and considering the full range of $t^{\prime }$ and $b^{\prime }$ flavor-mixing scenarios (with the lighter generations). Various characteristic mass-splitting choices are considered. With $m_{t^{\prime }}>m_{b^{\prime }}$ we find that CDF limits on the $b^{\prime }$ mass vary by no more than 10-20% with any choice of flavor-mixing, while for the $t^{\prime }$ mass, we typically find stronger bounds, in some cases up to $m_{t^{\prime }}>430$ GeV. For $m_{b^{\prime }}>m_{t^{\prime }}$ we find $m_{b^{\prime }}>380-430$ GeV, depending on the flavor-mixing and the size of the $m_{t^{\prime }}-m_{b^{\prime }}$ mass splitting.