Abstract:
Nonlinearities in King plots (KP) of isotope shifts (IS) can reveal the existence of beyond-standard-model (BSM) interactions that couple electrons and neutrons. However, it is crucial to distinguish higher-order standard model (SM) effects from BSM physics. We measure the IS of the transitions 3𝑃0→3𝑃1 in Ca14+ and 2𝑆1/2→2𝐷5/2 in Ca+ with sub-Hz precision as well as the nuclear mass ratios with relative uncertainties below 4 ×10−11 for the five stable, even isotopes of calcium (40,42,44,46,48Ca). Combined, these measurements yield a calcium KP nonlinearity with a significance of ∼103𝜎. Precision calculations show that the nonlinearity cannot be fully accounted for by the expected largest higher-order SM effect, the second-order mass shift, and identify the little-studied nuclear polarization as the only remaining SM contribution that may be large enough to explain it. Despite the observed nonlinearity, we improve existing KP-based constraints on a hypothetical Yukawa interaction for most of the new boson masses between 10 eV/c2 and 107 eV/c2.
M. Door, S. Eliseev, P. Filianin, J. Herkenhoff, K. Kromer, K. Blaum et al., „Nonlinear Calcium
King Plot Constrains New Bosons and Nuclear Properties“, Phys. Rev. Lett. 134, 233002
(2025).
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.233002
Related to Project B01, B02