Abstract
A high-intensity, low-emittance atomic muonium (M =\mu^+ + e^-=μ++e−) beam is being developed, which would enable improving the precision of M spectroscopy measurements, and may allow a direct observation of the M gravitational interaction. Measuring the free fall of M atoms would be the first test of the weak equivalence principle using elementary antimatter (\mu^+μ+) and a purely leptonic system. Such an experiment relies on the high intensity, continuous muon beams available at the Paul Scherrer Institute (PSI, Switzerland), and a proposed novel M source. In this paper, the theoretical motivation and principles of this experiment are described.
Highlights
Muonium (M) is a two-body exotic atom consisting of a positive anti-muon (μ+) and an electron (e−)
A high-intensity, low-emittance atomic muonium (M = μ+ + e−) beam is being developed, which would enable improving the precision of M spectroscopy measurements, and may allow a direct observation of the M gravitational interaction
Local Lorentz invariance (LLI): The outcome of any local non-gravitational experiment in a free-falling laboratory is independent of its velocity
Summary
Muonium (M) is a two-body exotic atom consisting of a positive anti-muon (μ+) and an electron (e−). Laser spectroscopy of the M 1S-2S transition [1, 2], and microwave spectroscopy of the M ground state hyperfine structure [3] provided precision measurements of fundamental constants (muon mass, magnetic moment), while searches for muonium-antimuonium conversion put limits on the strength of charged lepton number violation [4]. Improvements in these measurements especially 1S2S spectroscopy is strongly motivated by recent experiments measuring the anomalous muon g − 2 [5].
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