Evidence for production of single top quarks
Bibliographic record
Abstract
We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron $p\overline{p}$ collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a $0.9\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data set that have an electron or muon and missing transverse energy from the decay of a $W$ boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a $b$ hadron decay. The selected events are mostly backgrounds such as $W+\mathrm{\text{jets}}$ and $t\overline{t}$ events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}tb+X,tqb+X)=4.7\ifmmode\pm\else\textpm\fi{}1.3\text{ }\text{ }\mathrm{pb}$. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the $Wtb$ coupling and find $|{V}_{tb}{f}_{1}^{L}|={1.31}_{\ensuremath{-}0.21}^{+0.25}$, where ${f}_{1}^{L}$ is a generic vector coupling. This model-independent measurement translates into $0.68<|{V}_{tb}|\ensuremath{\le}1$ at the 95% C.L. in the standard model.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".