https://doi.org/10.1140/epjd/s10053-025-00959-2
Regular Article - Atomic Physics
Precision measurements of muonium and muonic helium hyperfine structure at J-PARC
1
Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization (KEK), 1-1 Oho, 305-0801, Tsukuba, Ibaraki, Japan
2
Materials and Life Science Division, J-PARC Center, 2-4 Shirakata, Tokai-mura, 319-1195, Naka-gun, Ibaraki, Japan
3
Materials Structure Science Program, Graduate Institute for Advanced Studies, SOKENDAI, 1-1 Oho, 305-0801, Tsukuba, Ibaraki, Japan
4
Cryogenics Science Center, High Energy Accelerator Research Organization (KEK), 1-1 Oho, 305-0801, Tsukuba, Ibaraki, Japan
5
Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, 464-8601, Nagoya, Aichi, Japan
6
Department of Physics, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, 950-2181, Niigata-shi, Niigata, Japan
7
Facility for Rare Isotope Beams, Michigan State University, 640 South Shaw Lane, 48824, East Lansing, Michigan, USA
8
Kobayashi-Maskawa Institute, Nagoya University, Furo-cho, Chikusa-ku, 464-8601, Nagoya, Aichi, Japan
9
Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata, Tokai-mura, 319-1195, Naka-gun, Ibaraki, Japan
10
Graduate School of Science and Engineering, Ibaraki University, 2-1-1 Bunkyo, 310-8512, Mito, Ibaraki, Japan
11
Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, T2N 1N4, Calgary, AB, Canada
12
School of Science, The University of Tokyo, 7-3-1 Hongo, 113-0033, Bunkyo-ku, Tokyo, Japan
13
Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi, 819-0395, Fukuoka, Japan
Received:
31
December
2024
Accepted:
16
January
2025
Published online:
14
March
2025
At the J-PARC Muon Science Facility (MUSE), the MuSEUM collaboration is now performing new precision measurements of the ground state hyperfine structure (HFS) of both muonium and muonic helium atoms. High-precision measurements of the muonium ground-state HFS are recognized as one of the most sensitive tools for testing bound-state quantum electrodynamics theory to precisely probe the standard model and determine fundamental constants of the positive muon magnetic moment and mass. The same technique can also be employed to measure muonic helium HFS, obtain the negative muon magnetic moment and mass, and test and improve the theory of the three-body atomic system. Measurements at zero magnetic field have already yielded more accurate results than previous experiments for both muonium and muonic helium atoms. High-field measurements are now ready to start collecting data using the world’s most intense pulsed muon beam at the MUSE H-line. We aim to improve the precision of previous measurements ten times for muonium and a hundred times or more for muonic helium. We review all the key developments for these new measurements, focusing on the high-field experiment, and report the latest results and prospects.
© The Author(s) 2025
corrected publication 2025
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
