Search for flavour-changing neutral-current interactions of a top quark and a gluon in pp collisions at√s=13 TeV with the ATLAS detector
Bibliographic record
Abstract
A search is presented for the production of a single top quark via left-handed flavour-changing neutral-current (FCNC) interactions of a top quark, a gluon and an up or charm quark. Two production processes are considered: $u+g\rightarrow t$ and $c+g\rightarrow t$. The analysis is based on proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of 139 fb$^{-1}$. Events with exactly one electron or muon, exactly one b-tagged jet and missing transverse momentum are selected, resembling the decay products of a singly produced top quark. Neural networks based on kinematic variables differentiate between events from the two signal processes and events from background processes. The measured data are consistent with the background-only hypothesis, and limits are set on the production cross-sections of the signal processes: $\sigma (u+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell \nu )<3.0\,$pb and $\sigma (c+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell \nu )<4.7\,$pb at the 95% confidence level, with $\mathcal {B}(W\rightarrow \ell \nu )=0.325$ being the sum of branching ratios of all three leptonic decay modes of the W boson. Based on the framework of an effective field theory, the cross-section limits are translated into limits on the strengths of the tug and tcg couplings occurring in the theory: $|C^{\,ut}_{uG}|/\Lambda ^2 < 0.057\,$TeV$^{-2}$ and $|C^{\,ct}_{uG}|/\Lambda ^2 < 0.14\,$TeV$^{-2}$. These bounds correspond to limits on the branching ratios of FCNC-induced top-quark decays: $\mathcal {B}(t\rightarrow u+g)< 0.61\times 10^{-4}$ and $\mathcal {B}(t\rightarrow c+g)< 3.7\times 10^{-4}$.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".