Measurement of lepton mass squared moments in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:msub><mml:mi>X</mml:mi><mml:mi>c</mml:mi></mml:msub><mml:mo>ℓ</mml:mo><mml:msub><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mo>ℓ</mml:mo></mml:msub></mml:math> decays with the Belle II experiment
Bibliographic record
Abstract
We present measurements of the first to fourth moments of the lepton mass squared ${q}^{2}$ of $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays for $\ensuremath{\ell}=e$, $\ensuremath{\mu}$ and with ${X}_{c}$ a hadronic system containing a charm quark. These results use a sample of electron-positron collisions at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance corresponding to $62.8\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity and collected by the Belle II 2 experiment in 2019 and 2020. To identify the ${X}_{c}$ system and reconstruct ${q}^{2}$, one of the $B$ mesons from an $\mathrm{\ensuremath{\Upsilon}}(4S)\ensuremath{\rightarrow}B\overline{B}$ decay is fully reconstructed in a hadronic decay mode using a multivariate $B$ tagging algorithm. We report raw and central moments for ${q}^{2}>1.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$ up to ${q}^{2}>8.5\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$, probing up to 77% of the accessible $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ phase space. This is the first measurement of moments in the experimentally challenging range of $[1.5,2.5]\text{ }\text{ }{\mathrm{GeV}}^{2}/{c}^{4}$. The results can be used for a new determination of $|{V}_{cb}|$ using inclusive $B\ensuremath{\rightarrow}{X}_{c}\ensuremath{\ell}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ decays.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.025 | 0.003 |
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".