Search for Heavy Bottomlike Quarks Decaying to an Electron or Muon and Jets in p(p)over-bar Collisions at root s=1.96 TeV

We report the most sensitive direct search for pair production of fourth-generation bottomlike 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 identified as due to a b or c quark), and an imbalance of transverse momentum by using data from b (b) over bar collisions collected by the CDF II detector at Fermilab with an integrated luminosity of 4: 8 fb(-1). We observe events consistent with background expectation, calculate upper limits on the b' pair-production cross section (sigma b (b) over bar less than or similar to 30 fb for m(b') > 375 GeV/c(2)), and exclude m(b') < 372 GeV/c(2) at 95% confidence level assuming a 100% branching ratio of b0 to tW.