Implications of absolute nuclear charge radii measurements for fundamental physics tests

High-precision isotope shift spectroscopy in heavy atoms and ions offers tabletop probes for physics Beyond the Standard Model (BSM). King plot analyses are particularly sensitive to new,

weakly-coupled bosons that would manifest as a deviation from linearity [1]. While experimental precision in isotope shift measurements has reached an extraordinary level, the interpretation of these results is limited by our knowledge of nuclear structure.

The challenge is to clearly distinguish a potential BSM signal from higher-order Standard Model effects, such as changes in nuclear deformation, which can also produce King plot nonlinearities. This requires precise knowledge of the nuclear charge distribution. The choice of input radius value impacts the interpretation of observed nonlinearities, potentially obscuring or mimicking a new physics signal and limiting the discovery potential of current and future experiments. Establishing a consistent set of absolute charge radii for an isotopic chain is thus very important. In this poster, we argue the constraints that the absolute nuclear charge measurements place on these BSM experiments, and how a slightly different value of the absolute nuclear charge radius would affect the results and interpretation of these experiments.

References

[1] Hur, Joonseok, et al. "Evidence of two-source king plot nonlinearity in spectroscopic search for new

boson." Physical Review Letters(2022)