Search for production of vector-like quark pairs and of four top quarks in the lepton plus jets final state in $pp$ collisions at $\\\\sqrt{s}=8$ TeV with the ATLAS detector
Bibliographic record
Abstract
A search is presented for pair production of vector-like quarks, both up-type ($T$) and down-type ($B$), as well as for four-top-quark production. The search is based on $pp$ collisions at $\\\\sqrt{s}=8$ TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 20.3 fb$^{-1}$. Data are analysed in the lepton plus jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and multiple jets. Dedicated analyses are performed targeting three cases: a $T$ quark with significant branching to a $W$ boson and a $b$ quark ($T\\\\bar{T} \\\\to Wb$+X), and both a $T$ quark and a $B$ quark with significant branching ratio to a Higgs boson and a third generation quark ($T\\\\bar{T} \\\\to Ht$+X and $B\\\\bar{B} \\\\to Hb$+X respectively). The analyses exploit characteristic features of the signals to discriminate against the dominant background from top quark pair production, such as the high total transverse momenta of all final state objects, the presence of boosted hadronically-decaying $W$ bosons, or the presence of Higgs bosons decaying into $b\\\\bar{b}$, resulting in high $b$-jet multiplicity. No significant excess of events above the Standard Model expectation is observed, and 95% CL lower limits are derived on the masses of the vector-like $T$ and $B$ quarks under several branching ratio hypotheses assuming contributions from $T \\\\to Wb$, $Zt$, $Ht$ and $B \\\\to Wt$, $Zb$, $Hb$ decays. The 95% CL observed lower limits on the $T$ quark mass range between 715 GeV and 950 GeV for all possible values of the branching ratios into the three possible decay modes, representing the most stringent constraints to date. Additionally, the most restrictive existing upper bounds on four-top-quark production are set in a number of new physics scenarios.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".