Search for Resonant Top-Antitop Production in the Lepton Plus Jets Decay Mode Using the Full CDF Data Set

This Letter reports a search for a narrow resonant state decaying into two $W$ bosons and two $b$ quarks where one $W$ boson decays leptonically and the other decays into a quark-antiquark pair. The search is particularly sensitive to top-antitop resonant production. We use the full data sample of proton-antiproton collisions at a center-of-mass energy of 1.96 TeV collected by the CDF II detector at the Fermilab Tevatron, corresponding to an integrated luminosity of $9.45{\mathrm{fb}}^{-1}$. No evidence for resonant production is found, and upper limits on the production cross section times branching ratio for a narrow resonant state are extracted. Within a specific benchmark model, we exclude a $Z^{\prime }$ boson with mass, $M_{Z^{\prime }}$, below $915\mathrm{GeV}/c^2$ decaying into a top-antitop pair at the 95% credibility level assuming a $Z^{\prime }$ boson decay width of ${\Gamma }_{Z^{\prime }}=0.012M_{Z^{\prime }}$. This is the most sensitive search for a narrow $q\overline{q}$-initiated $t\overline{t}$ resonance in the mass region below $750\mathrm{GeV}/c^2$.

Figure 1

Reconstructed $M_{t\overline{t}}$ for the three-jet events (left) and four-or-more-jet events (right). The distribution of the $M_{t\overline{t}}$ spectrum is on a linear scale, and the inset shows a logarithmic scale of the same distribution. The background expectation is normalized to the best fit to the data. The red histogram shows the expectation for a $600\mathrm{GeV}/c^2$ mass hypothesis for the leptophobic top-color resonance normalized to the predicted cross section.

Figure 2

Expected and observed upper limits on the production cross section times the branching ratio for a leptophobic top-color $Z^{\prime }$ boson in $9.45{\mathrm{fb}}^{-1}$ of CDF data. The dashed line is the median expected upper limit with the assumption of no signal, the black points are the observed limit, and the blue line is the cross section prediction for leptophobic top-color $Z^{\prime }$ boson [19] production.

Figure 3

Tevatron and LHC sensitivity comparison to new physics for narrow $t\overline{t}$ resonant final states, using the benchmark leptophobic top-color $Z^{\prime }$ model. The figure shows the expected upper limits on ${\sigma }_{Z^{\prime }}\mathrm{BR}(Z^{\prime }\to t\overline{t})$ divided by the theoretical prediction of ${\sigma }_{Z^{\prime }}\mathrm{BR}(Z^{\prime }\to t\overline{t})$ as a function of $M_{t\overline{t}}$. Dashed, dotted, and solid lines correspond to the expected upper limits of the most sensitive analyses to date from CDF, ATLAS, and CMS experiments, respectively.