Precision Determination of Isotope Shifts in Ytterbium and Implications for New Physics

We report measurements of isotope shifts for the five spinless Yb isotopes on the 6s(2) S-1(0) -> 5d6s D-1(2) transition using Doppler-free two-photon spectroscopy. We combine these data with existing measurements on two transitions in Yb+ [Counts et al. Phys. Rev. Lett. 125, 123002 (2020)], where deviation from King-plot linearity showed hints of a new bosonic force carrier at the 3 sigma level. The combined data strongly reduce the significance of the new-physics signal. We show that the observed nonlinearity in the joint Yb/Yb+ King-plot analysis can be accounted for by the deformation of the Yb nuclei.