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

Understand

Present limits on chiral fourth-generation quark masses $m_{b'}$ and $m_{t'}$ are broadly generalized and strengthened by combining both $t'$ and $b'$ decays and considering the full range of $t'$ and $b'$ flavor-mixing scenarios (with the lighter generations).

• Various characteristic mass-splitting choices are considered.
• With $m_{t'} > m_{b'}$ we find that CDF limits on the $b'$ mass vary by no more than 10-20% with any choice of flavor-mixing, while for the $t'$ mass, we typically find stronger bounds, in some cases up to $m_{t'} > 430$ GeV.
• For $m_{b'} > m_{t'}$ we find $m_{b'} > 380 - 430$ GeV, depending on the flavor-mixing and the size of the $m_{t'} - m_{b'}$ mass splitting.