Evidence for $s$-Channel Single-Top-Quark Production in Events with One Charged Lepton and Two Jets at CDF

We report evidence for $s$-channel single-top-quark production in proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96\mathrm{TeV}$ using a data set that corresponds to an integrated luminosity of $9.4{\mathrm{fb}}^{-1}$ collected by the Collider Detector at Fermilab. We select events consistent with the $s$-channel process including two jets and one leptonically decaying $W$ boson. The observed significance is 3.8 standard deviations with respect to the background-only prediction. Assuming a top-quark mass of $172.5\mathrm{GeV}/c^2$, we measure the $s$-channel cross section to be $1.41_{-0.42}^{+0.44}\mathrm{pb}$.

Figure 1

Distribution of invariant mass of the reconstructed top-quark candidates (left) and distribution of the neural-network output (right). We combine $b$-tag categories with comparable signal purity: $TT+TL$ for panels (a) and (b) and $T+LL$ for panels (c) and (d). Events in the pretag control sample are shown in panel (e). Statistical uncertainties are shown for the data points.

Figure 2

Posterior probability density distribution for the $s$-channel cross section measurement, with the SM prediction shown as the vertical dashed line.