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 a full range of $t^{\prime }$ and $b^{\prime }$ flavor-mixing scenarios with the lighter generations (to $1-\Vert V_{44}{\Vert }^2\approx {10}^{-13}$). Various characteristic mass-splitting choices are considered. With $m_{t^{\prime }}>m_{b^{\prime }}$ we find that CDF Collaboration 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 $m_{t^{\prime }}>430\mathrm{GeV}$. For $m_{b^{\prime }}>m_{t^{\prime }}$, we find $m_{b^{\prime }}>380–430\mathrm{GeV}$, depending on the flavor mixing and the size of the $m_{t^{\prime }}-m_{b^{\prime }}$ mass splitting.

• Received 10 May 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.111801