Distinguished EPJ Referees

Topical Review - Theory of the n=2 levels in muonic helium-3 ions

In this new article in EPJ D, Franke et al. review the present understanding of Lamb shift, fine- and hyperfine structure of the 2S and 2P states in muonic helium-3 ions in anticipation of the results of the first measurements of several 2S -> 2P transition frequencies in the muonic helium-3 ion, 3He+. This ion is the bound state of a single negative muon μ- and a bare helium-3 nucleus (helion), 3He++.

The authors present a term-by-term comparison of all available sources, including new, updated, and so far unpublished calculations, revealing reliable values and uncertainties of the QED and nuclear structure-dependent contributions to the Lamb shift and the hyperfine splitting. These values are essential for the determination of the helium RMS charge radius and the effects of the nuclear structure on the hyperfine splitting in 3He+. This review continues the authors’ series of theory summaries in light muonic atoms.

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