DATE2026.07.09 #Press Releases

New Method Demonstrated for Observing the Deep Structure of Atomic Nuclei Through a “Peephole”

Disclaimer: machine translated by DeepL which may contain errors.

— Hopes for Applications in Research into the Mysteries of Pions and Neutrinos —

Presentation Summary

Although atomic nuclei are composed of protons and neutrons, their structure is complex—for example, protons and neutrons are in motion, and atomic nuclei are not necessarily spherically symmetric.To gain a deeper understanding of this structure, it is known that observing the nucleus as it transitions from its most stable state (ground state) to a slightly higher-energy state (excited state) yields a wealth of information. Among these, the “0⁻” state (spin 0, negative parity) provides a crucial clue for understanding the nucleus, but it has been difficult to observe it efficiently in experiments.

Assistant Professor Masahiro Dozono of the Graduate School of Science at Kyoto University (at the time of the research: Project Assistant Professor at the Center for Nuclear Study, Graduate School of Science, The University of Tokyo); Tomohiro Uesaka, General Manager of the Nuclear Reaction Research Division at the Nishina Center for Accelerator-Based Science, RIKEN; Shinichiro Michimasa, Team Leader of the RI Beam Separation and Production Facility Team at the same center; Associate Professor Kentaro Yakoof the Center for Nuclear Study, Graduate School of Science, The University of Tokyo; and Professor Shinsuke Ota of the Research Center for Nuclear Physics, Osaka University—have developed a new nuclear reaction known as a “parity-transfer nuclear reaction” and succeeded in selectively observing the 0⁻ excited state of an atomic nucleus.In this method, a “parity change” generated by the incident particle is transferred to the target nucleus. This process can be likened to passing the baton in a relay race. The experiment was conducted at the RIKEN RI Beam Factory.

The “0⁻” state acts as a “window” through which the deep structure of the atomic nucleus can be observed. Since the properties of the pi meson—which is deeply involved in the forces binding the atomic nucleus together—are relatively clearly manifested in the 0⁻ state, investigating its behavior leads to a better understanding of the deep structure of the atomic nucleus.These results will enable systematic research on the 0⁻ state, for which sufficient data had not previously been obtained. Furthermore, the findings are expected to contribute to research aimed at determining the mass of neutrinos, which has not yet been established experimentally.

The research findings were published on June 30, 2026, in the Japanese international academic journal *Progress of Theoretical and Experimental Physics*.

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