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Nonlinear Calcium King Plot Constrains New Bosons and Nuclear Properties
Alexander Wilzewski1, Lukas J Spieß1, Malte Wehrheim1
1Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
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}.
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