Structure of the exotic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts/><mml:none/><mml:mn>9</mml:mn></mml:mmultiscripts></mml:math> nucleus from the no-core shell model with continuum
Bibliographic record
Abstract
Background: The exotic $^{9}\mathrm{He}$ nucleus, which presents one of the most extreme neutron-to-proton ratios, belongs to the $N=7$ isotonic chain famous for the phenomenon of ground-state parity inversion with decreasing number of protons. Consequently, it would be expected to have an unnatural (positive) parity ground state similar to $^{11}\mathrm{Be}$ and $^{10}\mathrm{Li}$. Despite many experimental and theoretical investigations, its structure remains uncertain. Apart from the fact that it is unbound, other properties including the spin and parity of its ground state, and the very existence of additional low-lying resonances are still a matter of debate.Purpose: In this work, we study the properties of $^{9}\mathrm{He}$ by analyzing the $n+^{8}\mathrm{He}$ continuum in the context of the ab initio no-core shell model with continuum (NCSMC) formalism with chiral nucleon-nucleon interactions as the only input.Methods: The NCSMC is a state-of-the-art approach for the ab initio description of light nuclei. With its capability to predict properties of bound states, resonances, and scattering states in a unified framework, the method is particularly well suited for the study of unbound nuclei such as $^{9}\mathrm{He}$.Results: Our analysis produces an unbound $^{9}\mathrm{He}$ nucleus. Two resonant states are found at the energies of $\ensuremath{\sim}1$ and $\ensuremath{\sim}3.5$ MeV, respectively, above the $n+^{8}\mathrm{He}$ breakup threshold. The first state has a spin-parity assignment of ${J}^{\ensuremath{\pi}}={1/2}^{\ensuremath{-}}$ and can be associated with the ground state of $^{9}\mathrm{He}$, while the second, broader state has a spin parity of ${3/2}^{\ensuremath{-}}$. No resonance is found in the ${1/2}^{+}$ channel, only a very weak attraction.Conclusions: We find that the $^{9}\mathrm{He}$ ground-state resonance has a negative parity and thus breaks the parity-inversion mechanism found in the $^{11}\mathrm{Be}$ and $^{10}\mathrm{Li}$ nuclei of the same $N=7$ isotonic chain.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 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".