Precision determination of isotope shifts in ytterbium and implications for new physics

TL;DR

This paper measures isotope shifts in ytterbium isotopes using Doppler-free spectroscopy, combining data with previous Yb+ measurements, and finds that nuclear deformation explains observed nonlinearities, reducing evidence for new physics.

Contribution

It provides precise isotope shift measurements in ytterbium and demonstrates that nuclear deformation accounts for King-plot nonlinearities, impacting new physics searches.

Findings

Narrowed the significance of potential new physics signals.

Attributed King-plot nonlinearity to nuclear deformation.

Enhanced understanding of isotope shifts in ytterbium.

Abstract

We report measurements of isotope shifts for the five spinless Yb isotopes on the $6s^2\,^1\textrm{S}_0 \rightarrow 5d6s\,^1\textrm{D}_2$ transition using Doppler-free two-photon spectroscopy. We combine these data with existing measurements on two transitions in Yb$^+$ [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 reduces 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.