High Energy Accelerator Research Organization

J-PARC Center

RIKEN

Graduate School of Science, The University of Tokyo

Graduate School of Arts and Sciences, The University of Tokyo

Summary

A research group led by Assistant Professor Sotaro Kanda and Professor Koichiro Shimomura at the Institute for Materials Structure Science, High Energy Accelerator Research Organization (KEK), in collaboration with KEK Institute for Particle and Nuclear Studies, RIKEN, The University of Tokyo, and others, has been conducting research at the Materials and Life Science Laboratory (MLSL), J-PARC Experimental Facility (MLF), Muon Science Experimental Facility (MUSE), succeeded in microwave spectroscopy of the ultrafine structure of muonium atoms in their ground state using an intense pulsed muon beam from the MLF. Muonium is a hydrogen-like atom composed of positively charged muons and electrons, and precise measurement of its hyperfine structure can verify the Standard Model of particle physics, including quantum electrodynamics, with extremely high precision. This experiment has the prospect of breaking the world record set at Los Alamos National Institute in 1999 by a factor of more than 10. This research result has been published in Physics Letters B .

Figure: Resonance curve of muonium hyperfine structure (HFS) obtained by the experiment.
The horizontal axis represents the microwave frequency, and the vertical axis represents the ratio of the number of positrons detected to the number of positrons changed by microwave irradiation. The closer the microwave frequency is to the frequency corresponding to the HFS, the larger the change in positron counts.

Associate Professor Hiroyuki Torii of the Department of Chemistry participated in the research results. For more information, please visit the website of the High Energy Accelerator Research Organization (KEK).