Nonlinear Calcium King Plot Constrains New Bosons and Nuclear Properties
Alexander Wilzewski, Lukas J. Spieß, Malte Wehrheim, Shuying Chen, S. A. King, P. Micke, Melina Filzinger, Martin Steinel, Nils Huntemann, Erik Benkler, Piet O. Schmidt, Luca Huber, Jeremy Flannery, Roland Matt, M. Stadler, R. Oswald, Fabian Schmid, Daniel Kienzler, Jonathan Home, Diana Prado Lopes Aude Craik, Menno Door, S. Eliseev, P. Filianin, Jost Herkenhoff, Kathrin Kromer, K. Blaum, V. A. Yerokhin, Igor A. Valuev, Natalia S. Oreshkina, Chunhai Lyu, S. Banerjee, Christoph H. Keitel, Zoltán Harman, J. C. Berengut, A. V. Viatkina, Jean-Paul Gilles, A. Surzhykov, Michael Rosner, J. R. Crespo López-Urrutia, Jan Richter, Agnese Mariotti, Elina Fuchs
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 ^{3}P_{0}→^{3}P_{1} in Ca^{14+} and ^{2}S_{1/2}→^{2}D_{5/2} 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 (^{40,42,44,46,48}Ca). Combined, these measurements yield a calcium KP nonlinearity with a significance of ∼10^{3}σ. 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/c^{2} and 10^{7} eV/c^{2}.