Search for Heavy Toplike Quarks Using Lepton Plus Jets Events in 1.96 TeV $p\overline{p}$ Collisions

We present the results of a search for pair production of a new heavy toplike quark $t^{\prime }$ decaying to a $W$ boson and another quark using the Collider Detector at Fermilab II detector in run II of the Tevatron $p\overline{p}$ collider. Using a data sample corresponding to $760{\mathrm{pb}}^{-1}$ of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed $t^{\prime }$ quark mass to a combination of standard model processes and $t^{\prime }$ pair production. We see no evidence for $t^{\prime }{\overline{t}}^{\prime }$ production, and we infer a lower limit of $256\mathrm{GeV}/c^2$ on the mass of the $t^{\prime }$ at 95% C.L. assuming standard strong couplings for the $t^{\prime }$.

Figure 1

Observed and predicted distributions of $M_{\mathrm{rec}}$ (above) and $H_T$ (below). The predicted distribution corresponds to that for a $250\mathrm{GeV}/c^2$ mass $t^{\prime }{\overline{t}}^{\prime }$ signal assuming a value of the cross section at 10 times the theoretical one. Note that in each plot the last bin is an overflow bin, and that the $W+\mathrm{\text{jets}}$ contribution also represents other similar backgrounds.

Figure 2

Observed and expected 95% C.L. upper limits on the cross section for $t^{\prime }{\overline{t}}^{\prime }$ production as a function of $t^{\prime }$ mass. The gray bands around the median expected limit show the $\pm 1$- and $\pm 2$-standard-deviation ranges. The theoretical prediction is also shown (assuming a 100% branching ratio to $Wq$).