Determination of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Al</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>27</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> Neutron Distribution Radius from a Parity-Violating Electron Scattering Measurement
Bibliographic record
Abstract
We report the first measurement of the parity-violating elastic electron scattering asymmetry on $^{27}\mathrm{Al}$. The $^{27}\mathrm{Al}$ elastic asymmetry is ${A}_{\mathrm{PV}}=2.16\ifmmode\pm\else\textpm\fi{}0.11(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.16(\text{syst})\text{ }\text{ }\mathrm{ppm}$, and was measured at $⟨{Q}^{2}⟩=0.02357\ifmmode\pm\else\textpm\fi{}0.00010\text{ }\text{ }{\mathrm{GeV}}^{2}$, $⟨{\ensuremath{\theta}}_{\mathrm{lab}}⟩=7.61\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}0.02\ifmmode^\circ\else\textdegree\fi{}$, and $⟨{E}_{\mathrm{lab}}⟩=1.157\text{ }\text{ }\mathrm{GeV}$ with the ${\mathrm{Q}}_{\mathrm{weak}}$ apparatus at Jefferson Lab. Predictions using a simple Born approximation as well as more sophisticated distorted-wave calculations are in good agreement with this result. From this asymmetry the $^{27}\mathrm{Al}$ neutron radius ${R}_{n}=2.89\ifmmode\pm\else\textpm\fi{}0.12\text{ }\text{ }\mathrm{fm}$ was determined using a many-models correlation technique. The corresponding neutron skin thickness ${R}_{n}\ensuremath{-}{R}_{p}=\ensuremath{-}0.04\ifmmode\pm\else\textpm\fi{}0.12\text{ }\text{ }\mathrm{fm}$ is small, as expected for a light nucleus with a neutron excess of only 1. This result thus serves as a successful benchmark for electroweak determinations of neutron radii on heavier nuclei. A tree-level approach was used to extract the $^{27}\mathrm{Al}$ weak radius ${R}_{w}=3.00\ifmmode\pm\else\textpm\fi{}0.15\text{ }\text{ }\mathrm{fm}$, and the weak skin thickness ${R}_{\mathrm{wk}}\ensuremath{-}{R}_{\mathrm{ch}}=\ensuremath{-}0.04\ifmmode\pm\else\textpm\fi{}0.15\text{ }\text{ }\mathrm{fm}$. The weak form factor at this ${Q}^{2}$ is ${F}_{\mathrm{wk}}=0.39\ifmmode\pm\else\textpm\fi{}0.04$.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.002 |
| Meta-epidemiology (broad) | 0.001 | 0.003 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.099 | 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 teacher head, 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".