Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson
Joonseok Hur🇺🇸 · Diana P. L. Aude Craik🇺🇸 · Ian Counts🇺🇸 · Eugene Knyazev🇺🇸 · Luke Caldwell🇺🇸 · Calvin Leung🇺🇸 · Swadha Pandey🇺🇸 · Julian C. Berengut🇦🇺 · Amy Geddes🇦🇺 · Witold Nazarewicz🇺🇸 · Paul-Gerhard Reinhard🇩🇪 · Akio Kawasaki🇯🇵 and 3 other authors
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 octupole transition of trapped Yb 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. The trends exhibited by experimental data are explained by nuclear density functional theory calculations with the Fayans functional. We also find, with 4.3 confidence, that there is a second distinct source of nonlinearity, and discuss its possible origin.