Generalised King Plots and the Search for New Physics Using Isotope Shift Spectroscopy.

King Plots are traditionally used to extract nuclear parameters from isotope shift measurements in a given atom or ion. It has long been assumed that a King Plot will be linear within the uncertainties of the experimental data from which they have been constructed. However, as the precision of atomic isotope shift measurements improve, the linearity of the King Plot may be broken. Previous work has proposed that non-linearities (NL) in King Plots may indicate the existence of physics beyond the Standard Model [1].

The search for new physics is complicated by the NL that arise from the experimental isotope mass uncertainties, as well as Standard Model sources of NL that may be observable at high precision [2]. It is possible to eliminate these spurious NL by creating a generalised version of the King Plot. The generalised King Plot can be constructed from atoms/ions with four or more isotope pairs and three different optical clock transitions [3]. The Yb/Yb+ system is a good candidate for the generalised King Plot, as it has multiple optical transitions measured at sub-Hz accuracy and five stable, spin zero isotopes. Therefore, It is possible to generate a King Plot of up to 4 dimensions with high precision in the Yb/Yb+ system and eliminate spurious NL.

[1] J. C. Berengut et al., Phys. Rev. Lett. 120, 091801 (2018).

[2] V. V. Flambaum, A. J. Geddes, and A. V. Viatkina, Phys. Rev. A 97, 032510 (2018).

[3] J. C. Berengut,1, C. Delaunay, A. Geddes, and Y. Soreq, Phys. Rev. Research 2, 043444 (2020).