An international team of researchers has detected signs of a rare η′-mesic nucleus, a fleeting particle trapped inside an atomic nucleus. This exotic state, observed in a high-precision experiment, suggests the η′ meson's mass decreases in dense nuclear matter. The finding could shed light on how matter acquires mass through the structure of space's vacuum.
Researchers at the GSI Helmholtzzentrum für Schwerionenforschung in Germany conducted the experiment by directing high-energy protons at a carbon target. This produced η′ mesons, some of which bound to the carbon nuclei, forming the predicted η′-mesic state. They analyzed deuterons emitted in the reaction using the Fragment Separator (FRS) and the WASA detector to identify decay signatures confirming the bound state, as lead author Ryohei Sekiya explained: “With our new experimental setup combining the FRS and the WASA, we can identify structures in the data that match theoretical signatures of η′-mesic nuclei. Our analysis suggests that these bound states were indeed formed.” 12C(p,d) Reaction near the η′-Meson Emission Threshold Measured in Coincidence with High-Momentum Protons,” published in Physical Review Letters. 12C(p,d) Reaction near the η′-Meson Emission Threshold Measured in Coincidence with High-Momentum Protons.” η′ meson is unusually heavy and its mass is expected to change inside nuclear matter, senior author Kenta Itahashi noted: “Observing this phenomenon would provide valuable information about how particle masses are generated in the universe.” η′ meson's mass appears to decrease within the nucleus, supporting theories on vacuum structure and mass generation. Itahashi added: “Our measurements provide important new clues about how mesons behave in nuclear matter.” The team plans further experiments for confirmation.
