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arXiv · 2606.11153

Quantum Monte Carlo calculations of Zemach moments in $A\leq 9$ nuclei

Garrett B. King·Sonia Bacca·Graham Chambers-Wall·Alex Gnech·Saori Pastore·Maria Piarulli·Robert B. Wiringa
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Abstract

Modern atomic spectroscopy has reached a level of precision at which nuclear-structure effects can no longer be neglected and must be quantified reliably. In particular, hyperfine splittings depend on the Zemach radius, which encodes the convolution of the nuclear charge and magnetization distributions. The third electric Zemach moment provides a related finite-size measure and enters the elastic two-photon-exchange contribution to the Lamb shift in muonic atoms. Here, we compute Zemach radii and other electromagnetic moments for light nuclei using quantum Monte Carlo techniques within modern \textit{ab initio} nuclear theory. Using Norfolk two- and three-body interactions derived within chiral effective field theory, we assess the model dependence and study the role of two-body currents. For $^6$Li, we obtain a Zemach radius larger than that extracted from atomic measurements, consistent with recent calculations, confirming that the discrepancy is not an artifact of the nuclear model. For $^9$Be, our results agree with experiment; the discrepancy of previous phenomenological evaluations is traced to a model-dependent input for the magnetic radius.

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Garrett B. King, Sonia Bacca, Graham Chambers-Wall, Alex Gnech, Saori Pastore, Maria Piarulli, Robert B. Wiringa. 2026-06-09. Quantum Monte Carlo calculations of Zemach moments in $A\leq 9$ nuclei. https://arxiv.org/abs/2606.11153

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