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arXiv · 2004.11383

Evidence for Nonlinear Isotope Shift in Yb$^+$ Search for New Boson

Ian Counts·Joonseok Hur·Diana P. L. Aude Craik·Honggi Jeon·Calvin Leung·Julian Berengut·Amy Geddes·Akio Kawasaki·Wonho Jhe·Vladan Vuletić
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Abstract

We measure isotope shifts for five Yb$^+$ isotopes with zero nuclear spin on two narrow optical quadrupole transitions ${}^2S_{1/2} \rightarrow {}^2D_{3/2}$, ${}^2S_{1/2} \rightarrow {}^2D_{5/2}$ with an accuracy of $\sim 300$ Hz. The corresponding King plot shows a $3 \times 10^{-7}$ deviation from linearity at the 3 $σ$ uncertainty level. Such a nonlinearity can indicate physics beyond the Standard Model (SM) in the form of a new bosonic force carrier, or arise from higher-order nuclear effects within the SM. We identify the quadratic field shift as a possible contributor to the nonlinearity at the observed scale, and show how the nonlinearity pattern can be used in future, more accurate measurements to separate a new-boson signal from nuclear effects.

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Ian Counts, Joonseok Hur, Diana P. L. Aude Craik, Honggi Jeon, Calvin Leung, Julian Berengut, Amy Geddes, Akio Kawasaki, Wonho Jhe, Vladan Vuletić. 2020-09-16. Evidence for Nonlinear Isotope Shift in Yb$^+$ Search for New Boson. https://doi.org/10.1103/physrevlett.125.123002

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