# The $\pi^0$ mass and the first experimental verification of Coulomb de-excitation in pionic hydrogen

### Submission summary

 Authors (as Contributors): Manfred Daum
Submission information
Preprint link: scipost_202105_00042v2
Date accepted: 2021-07-06
Date submitted: 2021-07-05 10:00
Submitted by: Daum, Manfred
Submitted to: SciPost Physics Proceedings
Proceedings issue: Review of Particle Physics at PSI
Ontological classification
Academic field: Physics
Specialties:
• High-Energy Physics - Experiment
Approach: Experimental

### Abstract

The most precise value for the $\pi^0$ mass was obtained from the measurement of the mass difference $m_{\pi^-}-m_{\pi^0} = 4.593\,64(48)$\,MeV/c$^2$ in the charge exchange reaction $\pi^-$p $\rightarrow \pi^0$n at PSI. With the most precise charged pion mass value, $m_{\pi^+} = 139.570\,21(14)$\,MeV/c$^2$ and the validity of the CPT theorem ($m_{\pi^-} = m_{\pi^+}$), a value $m_{\pi^0} = 134.976\,57(50)$\,MeV/c$^2$ is obtained. The measurements also revealed, for the first time, evidence of an unexpectedly large contribution from Coulomb de-excitation states during the pionic atom cascade.

Published as SciPost Phys. Proc. 5, 012 (2021)

### Submission & Refereeing History

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Resubmission scipost_202105_00042v2 on 5 July 2021
Submission scipost_202105_00042v1 on 29 May 2021