Abstract
Recent and ongoing developments of low energy muon beamlines are heralding a new era of precision Muonium spectroscopy. While past spectroscopic measurements of Muonium were performed at pulsed muon facilities and were statistically limited, the advent of continuous low energy muon beams, such as at the LEM beamline at PSI, paired with the development of efficient muon-muonium converters and laser advancements, will overcome these limitations. Current experiments presently underway at the LEM facility and in the near future at the muCool beamline, which is under development at PSI, aim to improve the precision of both the 1S-2S transition determination and Lamb shift by several orders of magnitude. In this Chapter we give an overview of the current status and future prospects of these activities at PSI, highlighting how their projected significance fits into a broader context of other ongoing efforts worldwide.
Highlights
The usefulness of precision spectroscopy for atomic systems with a hadronic nucleus is limited by our knowledge of quantum chromodynamics (QCD), which is not yet tractable at low energies
The availability of an intense 104/s μ+ beam in this energy range opens new possibilities for high precision M spectroscopy. In this Chapter we review the ongoing measurements of the 1S-2S transition and the Lamb shift (LS) of muonium in the context of the MuoniuM lAser SpectroScopy (Mu-MASS) experiment at PSI
Mμ = 206.768281(2)(3), me where the first uncertainty is from the experimental M ground-state hyperfine splittings measurement ∆νHFS [15], and the second is due to uncalculated QED terms [14], resulting in a combined relative uncertainty at a level 19 ppb
Summary
The usefulness of precision spectroscopy for atomic systems with a hadronic nucleus is limited by our knowledge of quantum chromodynamics (QCD), which is not yet tractable at low energies. The availability of an intense 104/s μ+ beam in this energy range opens new possibilities for high precision M spectroscopy In this Chapter we review the ongoing measurements of the 1S-2S transition and the Lamb shift (LS) of muonium in the context of the MuoniuM lAser SpectroScopy (Mu-MASS) experiment at PSI. In contrast to the hyperfine and gross-structure, the lamb shift in M is a pure bound-state QED correction, and so the desired precision to make a measurement interesting is less stringent This is especially true for high order recoil and radiative-recoil corrections, which due to the lower mass of M are much larger than in H. An improvement by factor of 100 or more on the current experimental accuracy of 1% will test QED corrections on the level of which they are currently tested by the HFS
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