Abstract
We measure isotope shifts for neutral Yb isotopes on an ultranarrow optical clock transition with an accuracy of a few hertz. Combined with one of the recently reported isotope-shift measurements of on two optical transitions, the result allows us to construct the King plots—a set of scaled isotope shifts data on two different optical transitions plotted in two-dimensional plane. When only the leading-order terms of isotope shifts are taken into account, a King plot should exhibit a linear relation as a result of elimination of the leading nuclear-size dependence. Extremely large nonlinearity unexplainable by a quadratic field shift is revealed, which was proposed previously as a source of the observed nonlinearity of the King plot. We further construct the generalized King plot with three optical transitions so that we can eliminate the contribution arising from a higher-order effect within the standard model. Our analysis of the generalized King plot shows a deviation from linearity at the level, indicating that there exist at least two higher-order contributions in the measured isotope shifts. Under reasonable assumptions, we obtain the upper bound of the product of the couplings for a new boson, mediating a force between electrons and neutrons— for the mass less than 1 keV—with the 95% confidence level, providing an important step toward probing new physics via isotope-shift spectroscopy.
2 More- Received 18 October 2021
- Accepted 16 March 2022
DOI:https://doi.org/10.1103/PhysRevX.12.021033
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
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Research News
Precision Nuclear Probes for New Physics
Published 15 July 2022
Tests of the standard model of particle physics using nuclear isotopes are becoming increasingly precise but they have a way to go before they can confirm the existence of any new particles.
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Popular Summary
Although the standard model successfully describes most phenomena in particle physics, it is not perfect, from both theoretical and experimental points of view. Physicists have been continuously searching for physics beyond this model in various energy ranges. Here, we demonstrate one unique approach via precise, low energy, atomic physics measurements.
Recently, a novel proposal to detect a new particle beyond the standard model—a particle that mediates a force between neutrons and electrons—attracted considerable attention. The proposal relies on the linear relation of the isotope shifts of different electronic transitions, known as King plot linearity. The new force carrier would manifest itself in an isotope-dependent shift of resonance frequencies, and the new particle would be probed by testing the breakdown of the King plot linearity.
Using a new measurement of the isotope shifts of neutral ytterbium atoms with an accuracy of about 1 Hz, we successfully construct the generalized King plot of three electronic transitions. By combining this result with previous work on the ion, we eliminate unknown contributions from the standard model that might mimic the nonlinearity from a new particle. From the remaining nonlinearity of this generalized King plot, we successfully evaluate the upper bound of the new boson coupling.
This work, combined with future isotope-shift measurements with similar precision, should provide the most stringent bound for seeking evidence of this new, proposed boson.