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arXiv · 2509.04674

Microwave Spectroscopy of the Muonium $2S_{1/2}-2P_{3/2}$ Fine Structure Interval

Philipp Blumer·Gianluca Janka·Svenja Geissmann·Iren Ignatov·Marcus Mähring·Zaher Salman·Andreas Suter·Edward Thorpe-Woods·Thomas Prokscha·Ben Ohayon·Paolo Crivelli
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Abstract

We report a microwave spectroscopy measurement of the muonium $2S_{1/2}-2P_{3/2}$ fine structure transition, yielding a transition frequency of $9871.0 \pm 7.0~\mathrm{MHz}$, in agreement with state-of-the-art QED predictions within one standard deviation. In combination with the recent Lamb shift result, the $2P_{1/2}-2P_{3/2}$ splitting is determined, improving the spectroscopic characterization of the $n=2$ manifold in muonium. These results provide a stringent test of bound-state QED in a purely leptonic system and establish a path toward future searches for Lorentz violation and muon-specific new physics.

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Philipp Blumer, Gianluca Janka, Svenja Geissmann, Iren Ignatov, Marcus Mähring, Zaher Salman, Andreas Suter, Edward Thorpe-Woods, Thomas Prokscha, Ben Ohayon, Paolo Crivelli. 2025-09-04. Microwave Spectroscopy of the Muonium $2S_{1/2}-2P_{3/2}$ Fine Structure Interval. https://arxiv.org/abs/2509.04674

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