Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevlett.131.253003

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.131.253003/fulltext

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

At J-PARC, the MuSEUM (Muonium Spectroscopy Experiment Using Microwave) collaboration aims to precisely measure the ground-state hyperfine splitting of muonium atoms arising from the muon and electron spins. The pulsed muon beam is stopped in a krypton gas cell to form muonium atoms. The transitions of spin states are induced with a microwave cavity, which are then measured by positron counters. After the previously performed successful measurements with a nearly-zero magnetic field, we are currently planning a measurement with the 2.9T magnetic field by measuring two Zeeman-split sub-levels, so that increased statistics will allow us to more precisely determine the transition frequency down to ∼1ppb. Moreover, a new microwave cavity with a unique geometry is being designed to perform the measurement at an even stronger field of 2.9T in the future.

DOI： 10.1088/1742-6596/2462/1/012019

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Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2462/1/012019/pdf

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Measurements of the muonic helium atom hyperfine structure (HFS) are a sensitive tool to test the theory of three-body atomic systems and bound-state quantum electrodynamics (QED) and to determine fundamental constants of the negative muon magnetic moment and mass. The world’s most intense pulsed negative muon beam at J-PARC MUSE brings an opportunity to improve previous measurements and test further CPT invariance by comparing the magnetic moments and masses of positive and negative muons. Test measurements at D-line are now in progress utilizing MuSEUM apparatus at zero field. The first results already have better accuracy than previous measurements in the 1980s. Also, the investigation of a new experimental approach to improve HFS measurements by repolarizing muonic helium atoms using a spin-exchange optical pumping (SEOP) technique was started. If successful, this would drastically improve the measurement accuracy.

DOI： 10.1088/1742-6596/2462/1/012023

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Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2462/1/012023/pdf

Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.37.021208

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Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

The measurement of the ground state hyperfine structure of muonic helium has the potential to improve the precision of the mass of the negative muon by a factor of 50 or more. The mass of the negative muon is very important because it enables us to test the CPT theorem by comparison with positive muon mass. We aim to measure the hyperfine structure of muonic helium with a precision 1000 times higher than previous experiments [1,2] using the highintensity muon beam at J-PARC and have already obtained results better than the current precision in zero-field measurements in a test experiment in March 2021. To further improve the precision, we plan to measure in a high magnetic field and incorporate a technique that can produce highly polarized muonic helium atom [3]. In this paper, we will report on these developments.

DOI： 10.1051/epjconf/202226201012

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Event date： 2023.5

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