Precision muon decay measurements and improved constraints on the weak interaction
Bibliographic record
Abstract
The TWIST Collaboration has completed its measurement of the three muon decay parameters $\ensuremath{\rho}$, $\ensuremath{\delta}$, and ${P}_{\ensuremath{\mu}}\ensuremath{\xi}$. This paper describes our determination of $\ensuremath{\rho}$, which governs the shape of the overall momentum spectrum, and $\ensuremath{\delta}$, which controls the momentum dependence of the parity-violating decay asymmetry. The results are $\ensuremath{\rho}=0.749\text{ }77\ifmmode\pm\else\textpm\fi{}0.000\text{ }12(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.000\text{ }23(\mathrm{syst})$ and $\ensuremath{\delta}=0.750\text{ }49\ifmmode\pm\else\textpm\fi{}0.000\text{ }21(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.000\text{ }27(\mathrm{syst})$. These are consistent with the value of $3/4$ given for both parameters in the standard model, and each is over a factor of 10 more precise than the measurements published prior to TWIST. Our final results on $\ensuremath{\rho}$, $\ensuremath{\delta}$, and ${P}_{\ensuremath{\mu}}\ensuremath{\xi}$ have been incorporated into a new global analysis of all available muon decay data, resulting in improved model-independent constraints on the possible weak interactions of right-handed particles.
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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 | 0.007 | 0.008 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.002 |
| Scholarly communication | 0.004 | 0.004 |
| Open science | 0.002 | 0.004 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.007 | 0.002 |
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".