# 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: PSI Particle Physics 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.

###### Current status:
Publication decision taken: accept

Editorial decision: For Journal SciPost Physics Proceedings: Publish
(status: Editorial decision fixed and (if required) accepted by authors)

### Submission & Refereeing History

Submission scipost_202102_00024v1 on 16 February 2021

## Reports on this Submission

### 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

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: -
• significance: -
• originality: -
• clarity: -
• formatting: -
• grammar: -