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Observation of Nonlinearity of Generalized King Plot in the Search for New Boson

Koki Ono, Yugo Saito, Taiki Ishiyama, Toshiya Higomoto, Tetsushi Takano, Yosuke Takasu, Yasuhiro Yamamoto, Minoru Tanaka, and Yoshiro Takahashi
Phys. Rev. X 12, 021033 – Published 10 May 2022
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Abstract

We measure isotope shifts for neutral Yb isotopes on an ultranarrow optical clock transition S10P03 with an accuracy of a few hertz. Combined with one of the recently reported isotope-shift measurements of Yb+ 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 3σ 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—|yeyn|/(c)<1×1010 for the mass less than 1 keV—with the 95% confidence level, providing an important step toward probing new physics via isotope-shift spectroscopy.

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  • 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

Physics Subject Headings (PhySH)

Atomic, Molecular & OpticalParticles & Fields

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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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Authors & Affiliations

Koki Ono1,*, Yugo Saito1, Taiki Ishiyama1, Toshiya Higomoto1, Tetsushi Takano2, Yosuke Takasu1, Yasuhiro Yamamoto3,4, Minoru Tanaka5, and Yoshiro Takahashi1

  • 1Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
  • 2NICHIA Corporation, 3-13-19, Moriya-Cho, Kanagawa-Ku, Yokohama, Kanagawa 221-0022, Japan
  • 3National Centre for Nuclear Research, Pasteura 7, Warsaw 02-093, Poland
  • 4Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
  • 5Department of Physics, Graduate School of Science, Osaka University, Osaka 560-0043, Japan

  • *koukiono3@yagura.scphys.kyoto-u.ac.jp

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.

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Vol. 12, Iss. 2 — April - June 2022

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