Groundbreaking experiments in Germany reveal the first evidence of the long-predicted pairing of carbon-11 nuclei and η’ mesons, shedding light on how the strongest forces in nature contribute to mass formation.
Sekiya et al. Experiments at Germany’s GSI/FAIR research center have uncovered evidence of exotic nuclear states. Image credit: J. Hosan, GSI/FAIR.
“In physics, we identify four fundamental forces: gravity, electromagnetism, strong interactions, and weak interactions,” stated Professor Kenta Itabashi from RIKEN and his team at Osaka University.
“Various bound systems are maintained by these forces. For instance, gravity holds the Earth and the moon together, while electromagnetic interactions bind positively charged atomic nuclei with negatively charged electrons.”
“The nucleus of an atom, composed of protons and neutrons, is held together by strong interactions.”
“In addition to protons and neutrons, which are each made up of three quarks, other particles, such as mesons, also participate in strong interactions.”
“Certain mesons carry a negative charge,” the physicists commented.
“In special instances, these mesons can displace electrons within an atom and bond to the nucleus via electromagnetic interactions.”
“However, some mesons, including the η’ meson, are electrically neutral.”
“Due to its lack of charge, the η’ meson cannot bond electromagnetically to an atom’s nucleus, relying instead on strong interactions for binding.”
“These situations, where strong interactions are the sole binding mechanism, are particularly intriguing as they allow us to gain insights into the nature of this force.”
In 2005, scientists anticipated the existence of meson-nuclear configurations formed solely by strong interactions.
However, thorough investigations into this exotic state had remained inconclusive until now.
Professor Itabashi and his collaborators conducted pioneering experiments at the GSI fragment separation facility in Germany.
“Our proton beam strikes the carbon-12 nucleus at approximately 96% of the speed of light, removing neutrons, forming deuterons, and proceeding forward,” the researchers explained.
“The residual carbon-11 nucleus is excited into a high-energy state, producing an η’ meson that occasionally binds with it. This results in a transient, bound quantum state.”
The implications of this experimental breakthrough extend well beyond the initial identification of an exotic nuclear state.
Simultaneously, it was demonstrated that the mass of the η’ meson diminishes within nuclear matter.
This finding enhances our comprehension of how meson mass is generated. The combined masses of the quarks in the η’ meson account for only about 1% of its total mass when unbound.
“Moving forward, our collaborative effort will conduct enhanced follow-up experiments, utilizing substantially more data to accurately gauge the spectroscopic properties of bound η’ meson nuclear systems, focusing on energy levels, binding energies, and decay widths,” the researchers concluded.
For further details, refer to their paper published in the Physical Review Letters.
_____
Takashi Sekiya et al. 2026. Excitation spectrum of the 12C(𝑝,𝑑) reaction near the 𝜂’-meson emission threshold measured simultaneously with high-momentum protons. Physics. Review Letters 136, 142501; doi: 10.1103/6vsl-ng7x
Source: www.sci.news
