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Current status and prospects of muonium spectroscopy at PSI

by B. Ohayon, Z. Burkley and P. Crivelli

This Submission thread is now published as SciPost Phys. Proc. 5, 029 (2021)

Submission summary

As Contributors: Paolo Crivelli
Preprint link: scipost_202106_00013v1
Date accepted: 2021-06-29
Date submitted: 2021-06-09 14:01
Submitted by: Crivelli, Paolo
Submitted to: SciPost Physics Proceedings
Proceedings issue: Review of Particle Physics at PSI
Academic field: Physics
  • Atomic, Molecular and Optical Physics - Experiment
  • High-Energy Physics - Experiment


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.

Published as SciPost Phys. Proc. 5, 029 (2021)

Reports on this Submission

Report 2 by Adrian Signer on 2021-6-22 (Invited Report)

  • Cite as: Adrian Signer, Report on arXiv:scipost_202106_00013v1, delivered 2021-06-22, doi: 10.21468/SciPost.Report.3100


We (the editors Cy Hoffman, Klaus Kirch, Adrian Signer) had the
opportunity to review an earlier draft of the article and were in
communication with the authors before the submission. All our comments
and suggestions have been taken into account. Hence, we think the
paper can now be published in the current form.

  • validity: -
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Anonymous Report 1 on 2021-6-18 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202106_00013v1, delivered 2021-06-18, doi: 10.21468/SciPost.Report.3079


1 - important future measurements of fundamental constants - primarily muon mass and muon-electron electric charge ratio
2-Opens new era of precision experiments on short-lived exotic purely leptonic atoms
3- novel technology for exotic atoms precision spectroscopy
4- High precision experimental test of Standard Model theory
5- Very well written
6- Most credible
7- ample references to important work in the field


1- no particular weaknesses
2-unfortunately, due to space restrictions some interesting details could not be further elaborated on


The authors provide a very well written report on precision atomic spectroscopy in the exotic, purely leptonic muonium atom. A crisp short review of the field is given. Based on this possible future experiments on laser spectroscopy of the muonium 1s-2s transition and the Lamb-shift in the n=2 level are described as well as measurements of the ground state hyperfine structure splitting are sketched. The importance of the expected results for other experiments in the field is worked. The possibility to obtain precise and in some cases substantially improved values for fundamental constants like the muon mass and the muon-electron electric charge ratio are explained and the indispensability of such precise values for a bias-free interpretation of the ongoing muon g-2 experiments at Fermilab and JPARC are addressed.

Despite a strong effort I couldn't spot any point to be criticized at all.
The only most minor correction required at all is for me in line 124, where the text overshoots onto the right margin.

The authors can be congratulated to such a beautiful article which puts many precision experiments into a powerful reference frame. The article should be published contentwise as is with no modifications.

Requested changes


  • validity: top
  • significance: top
  • originality: top
  • clarity: top
  • formatting: excellent
  • grammar: good

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