Test of lepton flavor universality with measurements of ▫$R(D^+)$▫ and ▫$R(D^{ast +})$▫ using semileptonic tagging at the Belle II experiment
Bibliographic record
Abstract
We report measurements of the ratios of branching fractions RðD ðÃÞþ Þ ¼ Bð B0 → D ðÃÞþ τ -ντ Þ= Bð B0 → D ðÃÞþ l -νl Þ, where l denotes either an electron or a muon.These ratios test the universality of the charged-current weak interaction.The results are based on a 365 fb -1 data sample collected with the Belle II detector at the SuperKEKB e þ e -collider, which operates at a center-of-mass energy corresponding to the ϒð4SÞ resonance, just above the threshold for B B production.Signal candidates are reconstructed by selecting events in which the companion B meson from the ϒð4SÞ → B B decay is identified in semileptonic modes.The τ lepton is reconstructed via its leptonic decays.We obtain RðD þ Þ ¼ 0.418 þ0.075 -0.073 ðstatÞ þ0.049 -0.056 ðsystÞ and RðD Ãþ Þ ¼ 0.306 þ0.035 -0.033 ðstatÞ þ0.016 -0.018 ðsystÞ, which are consistent with world average values.Accounting for the correlation between them, these values differ from the Standard Model expectation by a collective significance of 1.7 standard deviations.
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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 | 0.004 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".