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

TL;DR

This paper establishes comprehensive lower mass limits for hypothetical fourth-generation quarks by analyzing various decay and mixing scenarios, significantly strengthening previous bounds and covering a broad parameter space.

Contribution

It generalizes and strengthens existing mass limits for fourth-generation quarks by considering all decay modes and flavor-mixing scenarios, including different mass splittings.

Findings

$m_{b'}$ > 380-430 GeV depending on scenario

$m_{t'}$ > 430 GeV in some cases

Limits vary by only 10-20% with mixing variations

Abstract

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.