A huge discrepancy between the observed hyperfine splitting in highly-ionized bismuth-209 atoms and the expected value could be a calculation error rather than evidence for new physics. That is the conclusion of Leonid Skripnikov at St Petersburg State University in Russia and colleagues, who have shown that the magnetic moment of the bismuth-209 nucleus – which is used to calculate the hyperfine splitting — is much smaller than the currently accepted value.
Hyperfine splitting is a small shift in electron energy levels that arises because of the interaction between the dipole magnetic moment of the atomic nucleus and the orbital motion of the electrons. Very precise spectroscopic measurements of hyperfine splitting offer a way of testing quantum electrodynamics (QED). Finding discrepancies between QED and experimental observations could point towards physics beyond the Standard Model of particle physics.
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