Search for heavy toplike quarks using lepton plus jets events in 1.96 TeV pp̄ collisions

We present the results of a search for pair productionof a new heavy toplike quark t' decaying to a W boson and another quark using the Collider Detectorat FermilabII detector in run II of the Tevatronp (p) over bar collider. Using a data sample corresponding to 760 pb(-1) of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t' quark mass to a combination of standard model processes and t' pair production. We see no evidence for t'(t) over bar' production, and we infer a lower limit of 256 GeV/c(2) on the mass of the t(') at 95% C.L. assuming standard strong couplings for the t'.