Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson

Optical precision spectroscopy of isotope shifts can be used to test for new forces beyond the standard model, and to determine basic properties of atomic nuclei. We measure isotope shifts on the highly forbidden S-2(1/2) -> F-2(7/2) octupole transition of trapped Yb-168,170,172,174,(176) ions. When combined with previous measurements in Yb+ and very recent measurements in Yb, the data reveal a King plot nonlinearity of up to 240 sigma. The trends exhibited by experimental data are explained by nuclear density functional theory calculations with the Fayans functional. We also find, with 4.3 sigma confidence, that there is a second distinct source of nonlinearity, and discuss its possible origin.

Automated summary

Using optical precision spectroscopy to test isotope shifts, this study explores new forces and basic properties of atomic nuclei. The data reveal nonlinearity in the King plot and a second distinct source of nonlinearity, trends that can be explained through nuclear density functional theory calculations.