Shielded inner-shell transitions in atomic samarium for tests of fundamental physics
Abstract
Forbidden atomic transitions provide some of the most stringent low-energy tests of physics beyond the Standard Model, with sensitivity set by the interplay between the sought-for signals and systematics suppressed by symmetry. Here we identify the previously unobserved 4f66s2 5D0 level of neutral samarium at 14 564.90(2) cm−1, opening the 7F0→5D0 inner-shell transition for precision spectroscopy. Candidate lines extracted from dual-comb absorption spectra were assigned using double-resonance population-depletion and sequential-excitation measurements. The observed pressure broadening, 0.12(2) MHz/torr, and pressure shift, −0.145(4) MHz/torr, indicate an inner-shell 4f-transition shielded from external perturbations. Many-body calculations predict a metastable lifetime in the range $120−200\,\mathrm{ms}$, corresponding to a quality factor of order 𝒬∼1014, large sensitivity coefficients for variation of the fine-structure constant, and a nuclear-spin-dependent parity-violation amplitude comparable to that of cesium. Crucially, the J=0→ J=0 selection rule suppresses by symmetry both the nuclear-spin-independent parity-violation channel and the M1 and E2 backgrounds that complicated previous heavy-atom experiments, yielding a uniquely clean window onto the nuclear anapole moment. The two stable spin-7/2 isotopes of samarium provide a remarkable opportunity to largely cancel atomic-structure uncertainties by measuring the ratio of parity-violation effects in the two isotopes. These results establish neutral samarium as a platform for inner-shell precision spectroscopy and tests of physics beyond the Standard Model.
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BibTeX
@misc{aramyan2026shielded,
title = {{Shielded inner-shell transitions in atomic samarium for tests of fundamental physics}},
author = {R. Aramyan and D. Budker and V. A. Dzuba and V. V. Flambaum and S. G. Porsev and M. S. Safronova and O. Tretiak and K. Zhang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.22318},
eprint = {2605.22318},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.22318},
}
RIS
TY - UNPB
TI - Shielded inner-shell transitions in atomic samarium for tests of fundamental physics
AU - R. Aramyan
AU - D. Budker
AU - V. A. Dzuba
AU - V. V. Flambaum
AU - S. G. Porsev
AU - M. S. Safronova
AU - O. Tretiak
AU - K. Zhang
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2605.22318
UR - https://arxiv.org/abs/2605.22318
AB - Forbidden atomic transitions provide some of the most stringent low-energy tests of physics beyond the Standard Model, with sensitivity set by the interplay between the sought-for signals and systematics suppressed by symmetry. Here we identify the previously unobserved 4f^66s^2 ^5D_0 level of neutral samarium at 14 564.90(2) cm^−1, opening the ^7F_0→^5D_0 inner-shell transition for precision spectroscopy. Candidate lines extracted from dual-comb absorption spectra were assigned using double-resonance population-depletion and sequential-excitation measurements. The observed pressure broadening, 0.12(2) MHz/torr, and pressure shift, −0.145(4) MHz/torr, indicate an inner-shell 4f-transition shielded from external perturbations. Many-body calculations predict a metastable lifetime in the range $120−200\,\mathrm{ms}$, corresponding to a quality factor of order 𝒬∼10^14, large sensitivity coefficients for variation of the fine-structure constant, and a nuclear-spin-dependent parity-violation amplitude comparable to that of cesium. Crucially, the J=0→ J=0 selection rule suppresses by symmetry both the nuclear-spin-independent parity-violation channel and the M1 and E2 backgrounds that complicated previous heavy-atom experiments, yielding a uniquely clean window onto the nuclear anapole moment. The two stable spin-7/2 isotopes of samarium provide a remarkable opportunity to largely cancel atomic-structure uncertainties by measuring the ratio of parity-violation effects in the two isotopes. These results establish neutral samarium as a platform for inner-shell precision spectroscopy and tests of physics beyond the Standard Model.
ER -