# The mass of the $\pi^-$

### Submission summary

 As Contributors: Detlev Gotta Preprint link: scipost_202102_00019v1 Date submitted: 2021-02-11 12:54 Submitted by: Gotta, Detlev Submitted to: SciPost Physics Proceedings Proceedings issue: PSI Particle Physics Academic field: Physics Specialties: Nuclear Physics - Experiment Approach: Experimental

### Abstract

The most precise values of the mass of the negatively charged pion have been determined from several measurements of X-ray wavelengths for transitions in pionic atoms at PSI. The Particle Data Group gives the average $m_{\pi^-}= (139.570 61 \pm 0.000 24) MeV/c^2$.

###### Current status:
Editor-in-charge assigned

### Submission & Refereeing History

Submission scipost_202102_00019v1 on 11 February 2021

## Reports on this Submission

### Report

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: -

### Strengths

1- comprehensive review of the experiments that lead to a precise determination of the pion mass
2- all important papers about pion mass measurements and related objects are well referenced
3- the history of original discrepancies with other observations (p_mu), and how this was eventually resolved, is nicely and well reported
4- the most important measured spectra and the final results of pion mass values are well documented

### Weaknesses

1- some accuracies given should be better explained, see requested changes
2- a general conclusion at the paper end is missing and might be beneficial

### Report

The authors have written a comprehensive and interesting to read review of the history of the most precise pion mass measurements at the meson beams of PSI. This paper absolutely qualifies the acceptance criteria of this journal in style an content. Apart from a few minor details that might need better explanation, I recommend publication of this paper.

### Requested changes

1- introduction: the section about eq (10.1) should somehow be referenced
2- end of introduction (line 19): "<=+-1meV" - please explain of what
3-first sentence chapter 10.2 (line 22): "precision of about 1 ppm" please explain of what
4- page 3 bottom (line 84): "accuracy of 0.4%" please explain of what

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

Author Detlev Gotta on 2021-02-23
(in reply to Report 1 by Claude Petitjean on 2021-02-17)
Category:
correction

The changes suggested by the referee have been included. A new version is produced. The corresponding file of the new version is attached: piM_corr_2021_02_21.pdf

Changes in the text are as following (all line numbers refer to the new version) line number 13 reference related to eq. (10.1) according to referee remark 1 20-21 supplement according to referee remark 2 24 supplement according to referee remark 3 89 supplement according to referee remark 4

91-102 In view of the remark "Weakness" we added two short paragraphs as general conclusion which include more additional references.