# Muonium-Antimuonium Conversion

### Submission summary

 As Contributors: Lorenz Willmann Preprint link: scipost_202102_00024v1 Date accepted: 2021-04-28 Date submitted: 2021-02-16 17:41 Submitted by: Willmann, Lorenz Submitted to: SciPost Physics Proceedings Proceedings issue: Review of Particle Physics at PSI Academic field: Physics Specialties: Atomic, Molecular and Optical Physics - Experiment High-Energy Physics - Experiment Approach: Experimental

### Abstract

The MACS experiment performed at PSI in the 1990s provided an yet unchallenged upper bound on the probability for a spontaneous conversion of the muonium atom, ${\rm M=}$($\rm{\mu^+e^-}$) , into its antiatom, antimuonium ${\overline{\rm{M}} = }$($\rm{\mu^-e^+})$. It comprises the culmination of a series of measurements at various accelerator laboratories worldwide. The experimental limits on the process have provided input and steering for the further development of a variety of theoretical models beyond the standard theory, in particular for models which address lepton number violating processes and matter-antimatter oscillations. Several models beyond the standard theory could be strongly disfavored. There is interest in a new measurement and improved sensitivity could be reached by exploiting the time evolution of the conversion process, e.g., at intense pulsed muonium sources.

Published as SciPost Phys. Proc. 5, 009 (2021)

### Submission & Refereeing History

Submission scipost_202102_00024v1 on 16 February 2021

## Reports on this Submission

### Anonymous Report 2 on 2021-4-21 (Invited Report)

• Cite as: Anonymous, Report on arXiv:scipost_202102_00024v1, delivered 2021-04-21, doi: 10.21468/SciPost.Report.2814

### Strengths

The authors of this manuscript:
1- Provided a great summary of the field, including the motivation from the theoretical background.
2- Described concisely the previous experiment on muonium-antimuonium conversion (MACS, utilising the SINDRUM I magnet).
3 - Pointed out the most relevant source of background (muon decay related systematics).
4 - Suggested a new revised experiment using intense pulsed muon sources.
5 - Gave an estimate on the beam requirements on the pulsed source (several 10 kHz with μ+ bunches of up to ≈ μs length).
6 - Estimated the improvement of a revised experiment in exclusion for new physics (2 OM).

### Weaknesses

1 - The estimations in point 5 and 6 (from the above list of "Strengths") and the suggested new experiment were not introduced in detail. We need to note however that this might be beyond the scope of the present Proceedings.

### Report

I recommend the publication of this manuscript in the SciPost Physics Proceedings in its present form.

• validity: high
• significance: top
• originality: high
• clarity: top
• formatting: perfect
• grammar: excellent

### Report 1 by Adrian Signer on 2021-2-26 (Invited Report)

• Cite as: Adrian Signer, Report on arXiv:scipost_202102_00024v1, delivered 2021-02-26, doi: 10.21468/SciPost.Report.2623