New Evidence of ?´-Mesic Nuclei and the Origins of Mass

Recent experiments have provided evidence for the existence of ?´-mesic nuclei, a previously unobserved exotic state that may enhance our understanding of how mass originates from the vacuum structure of the universe. This research, conducted by an international team and published in *Physical Review Letters*, explores the fundamental question of mass generation, which remains a central topic in physics.

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To investigate ?´-mesic nuclei, researchers conducted a high-precision experiment at the GSI Helmholtzzentrum für Schwerionenforschung in Germany. They directed a beam of high-energy protons at a carbon target, which excited the carbon nuclei and produced ?´ mesons. These mesons, which are composed of a quark and an antiquark, can become briefly trapped within atomic nuclei, forming bound systems known as mesic nuclei. The team utilized a high-resolution instrument called the Fragment Separator (FRS) to measure the excitation energy of the carbon nuclei and a detector named WASA to track high-energy protons, identifying signals indicative of ?´ meson formation.

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The results suggest that the mass of the ?´ meson may decrease when it exists inside nuclear matter, aligning with theoretical predictions. Lead author Ryohei Sekiya noted, “With our new experimental setup combining the FRS and the WASA, we can identify structures in the data that match theoretical signatures of ?´-mesic nuclei.” This finding provides rare experimental evidence of how particle properties change under extreme conditions, contributing to a deeper understanding of the strong nuclear force and the behavior of the vacuum in dense environments.

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Senior author Kenta Itahashi emphasized the significance of these measurements, stating, “This brings us closer to answering deep, fundamental questions about how matter acquires mass, as well as how the vacuum structure changes inside atomic nuclei.”

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The research team plans to conduct further experiments aimed at improving measurement precision and searching for additional decay signals to confirm the existence of ?´-mesic nuclei. Each new result will refine our understanding of the fundamental laws that govern the universe.

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This study was supported by various institutions, including the Japan Society for the Promotion of Science, Jagiellonian University, Proyectos I+D+i 2020, the Community of Madrid, MCIN, GSI Helmholtzzentrum für Schwerionenforschung, Javna Agencija za Raziskovalno Dejavnost RS, RIKEN, Japan Science and Technology Agency, and the European Union.

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• “Our measurements provide important new clues about how mesons behave in nuclear matter,” — Kenta Itahashi, Senior Author

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• “With our new experimental setup combining the FRS and the WASA, we can identify structures in the data that match theoretical signatures of ?´-mesic nuclei,” — Ryohei Sekiya, Lead Author

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