Search for the neutral current top quark decay<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>t</mml:mi><mml:mo>→</mml:mo><mml:mi>Z</mml:mi><mml:mi>c</mml:mi></mml:math>using the ratio of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi><mml:mtext mathvariant="normal">-boson</mml:mtext><mml:mo>+</mml:mo><mml:mn>4</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mtext mathvariant="normal">jets</mml:mtext></mml:math>to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>W</mml:mi><mml:mtext mathvariant="normal">-boson</mml:mtext><mml:mo>+</mml:mo><mml:mn>4</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mtext mathvariant="normal">jets</mml:mtext></mml:math>production
Bibliographic record
Abstract
We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay $t\ensuremath{\rightarrow}Zc$ using a technique employing ratios of $W$ and $Z$ production, measured in $p\overline{p}$ data corresponding to an integrated luminosity of $1.52\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The analysis uses a comparison of two decay chains, $p\overline{p}\ensuremath{\rightarrow}t\overline{t}\ensuremath{\rightarrow}WbWb\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\nu}bjjb$ and $p\overline{p}\ensuremath{\rightarrow}t\overline{t}\ensuremath{\rightarrow}ZcWb\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\ell}cjjb$, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multiyear data set using another ratio of $W$ and $Z$ production, in this case the observed ratio of inclusive production of $W$ to $Z$ bosons. To improve the discrimination against standard model backgrounds to top-quark decays, we calculate the top-quark mass for each event with two leptons and four jets assuming it is a $t\overline{t}$ event with one of the top quarks decaying to $Zc$. For additional background discrimination we require at least one jet to be identified as originating from a $b$ quark. No significant signal is found and we set an upper limit on the FCNC branching ratio $\mathrm{Br}(t\ensuremath{\rightarrow}Zc)$ using a likelihood constructed from the $\ensuremath{\ell}\ensuremath{\ell}cjjb$ top-quark mass distribution and the number of $\ensuremath{\ell}\ensuremath{\nu}bjjb$ events. Limits are set as a function of the helicity of the $Z$ boson produced in the FCNC decay. For 100% longitudinally-polarized $Z$ bosons we find limits of 8.3% and 9.3% (95% C.L.) depending on the assumptions regarding the theoretical top-quark pair production cross section.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.037 | 0.008 |
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".