Direct Extraction of Nuclear Structure Information Using Precision Lithium-Ion Spectroscopy

TL;DR

This study uses high-precision lithium-ion spectroscopy to directly measure nuclear structure parameters, revealing discrepancies with existing theories and molecular data, thereby advancing nuclear physics understanding.

Contribution

It presents the first high-precision measurements of lithium ion hyperfine splittings that directly extract nuclear parameters, highlighting inconsistencies with prior data and supporting nuclear theory.

Findings

Significant deviations in electric quadrupole moments from previous values.

High-precision hyperfine measurements at 10 kHz level.

Support for nuclear structure theories through independent calculations.

Abstract

Accurately describing nuclear interactions within atomic nuclei remains a challenge, which hinders our exploration of new physics beyond the Standard Model. However, these nuclear interactions can be characterized by nuclear parameters such as the Zemach radius and the electric quadrupole moment, which are reflected in atomic spectra. Our work has achieved high-precision measurements of lithium ion hyperfine splittings at the level of $10$~kHz, and directly extracted these important nuclear structure parameters. We observed significant discrepancies between our results and both nuclear theory and molecular spectra regarding the electric quadrupole moment. The result for $^7$Li deviated by $2.3\sigma$ from the currently recommended value, whereas the result for $^6$Li deviated by up to $6.2\sigma$ from the recommended value determined by molecular spectroscopy. These discrepancies motivated us to conduct independent calculations based on nuclear structure theory, which provided support for the results obtained from ion spectroscopy. Our results provide valuable information for characterizing nuclear forces, serve as sensitive benchmarks for testing nuclear structure theories, and enable critical comparisons with both electron-nuclear scattering and molecular spectroscopy.