Measurement of the Single Top Quark Production Cross Section and $|V_{tb}|$ in Events with One Charged Lepton, Large Missing Transverse Energy, and Jets at CDF

We report a measurement of single top quark production in proton-antiproton collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$ using a data set corresponding to $7.5{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the Collider Detector at Fermilab. We select events consistent with the single top quark decay process $t\to Wb\to \ell \nu b$ by requiring the presence of an electron or muon, a large imbalance of transverse momentum indicating the presence of a neutrino, and two or three jets including at least one originating from a bottom quark. An artificial neural network is used to discriminate the signal from backgrounds. We measure a single top quark production cross section of $3.04_{-0.53}^{+0.57}\mathrm{pb}$ and set a lower limit on the magnitude of the coupling between the top quark and bottom quark $|V_{\mathit{t}\mathit{b}}|>0.78$ at the 95% credibility level.

Figure 1

Distribution of $\mathrm{\Delta }R(\overrightarrow{j_1},\overrightarrow{j_2})$ for the two most energetic jets in the $W+2$ jet pretag sample (a) before reweighting and (b) after reweighting. (c) The weight factor, which ranges up to 1.4 at large $\mathrm{\Delta }R$.

Figure 2

Comparison of the data with the sum of the predictions of the NN output for the combined two- and three-jet signal regions. The signal $+$ background model is fit to the data. The uncertainty associated with the sum of the predictions (after fitting) is indicated by the grey shaded region in each bin. The inset shows a magnification of the region for which the NN discriminant ranges from 0.8 to 1.0, where the single top quark contribution is larger.

Figure 3

Results of the two-dimensional fit for ${\sigma }_s$ and ${\sigma }_{t+\mathit{W}\mathit{t}}$. The black circle shows the best-fit value, and the 68.3%, 95.5%, and 99.7% credibility regions are shown as shaded areas. The standard model (SM) predictions are also indicated with their theoretical uncertainties.