Search for Resonances Decaying to Top and Bottom Quarks with the CDF Experiment

We report on a search for charged massive resonances decaying to top ($t$) and bottom ($b$) quarks in the full data set of proton-antiproton collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of $9.5{\mathrm{fb}}^{-1}$. No significant excess above the standard model background prediction is observed. We set 95% Bayesian credibility mass-dependent upper limits on the heavy charged-particle production cross section times branching ratio to $tb$. Using a standard model extension with a $W^{\prime }\to tb$ and left-right-symmetric couplings as a benchmark model, we constrain the $W^{\prime }$ mass and couplings in the $300–900\mathrm{GeV}/c^2$ range. The limits presented here are the most stringent for a charged resonance with mass in the range $300–600\mathrm{GeV}/c^2$ decaying to top and bottom quarks.

Figure 1

Expected and observed final discriminant distributions in the signal region. The distribution for a $W^{\prime }$ boson with $300\mathrm{GeV}/c^2$ mass and SM couplings is overlaid. The signal is normalized to a cross section times branching ratio of 3 pb. Plots show the discriminant in the following subsamples: 1T two-jet (a), 1T three-jet (b), TL two-jet (c), TL three-jet (d), TT two-jet (e), and TT (f) three-jet events.

Figure 2

Observed (solid line) and expected (dotted line) upper limits on $\sigma (p\overline{p}\to W^{\prime })\times \mathcal{B}(W^{\prime }\to tb)$, with $\pm 1\sigma$ and $\pm 2\sigma$ credibility intervals, divided by the theoretical predictions for a right-handed $W^{\prime }$ boson with SM-like couplings in the scenario where the leptonic decay mode $W^{\prime }\to \ell \nu$ is forbidden (dashed line). The CDF limits are compared with limits from the latest $W^{\prime }$ searches from ATLAS, CMS, and D0 [8, 9, 10]. The ATLAS (CMS) Collaboration excludes this model for $W^{\prime }$ masses up to 1.9(2.1) TeV.

Figure 3

Observed and expected 95% C.L. upper limits on the coupling strength of a right-handed $W^{\prime }$ boson compared to the SM $W$-boson coupling, $g_{W^{\prime }}/g_W$, as functions of $M_{W^{\prime }}$ in cases where the leptonic decay mode $W^{\prime }\to \ell \nu$ is forbidden. The region above each line is excluded. The CDF limits are compared with limits from the latest $W^{\prime }$ searches from ATLAS, CMS, and D0 [8, 9, 10]. The vertical part in each boundary region of the plot represents the minimum masses for which bounds are quoted.