We report the most sensitive direct search for pair production of fourth-generation bottom-like
chiral quarks (b) each decaying promptly to tW. We search for an excess of events with an electron
or muon, at least five jets (one indentified as due to a b or c quark) and an imbalance of transverse
momentum using data from p? collisions collected by the CDF II detector at Fermilab with an