今日吃瓜

A research team led by Associate Professor Sun Yelei from the School of Physics at 今日吃瓜, in collaboration with international partners, has identified for the first time a universal three-body s-wave resonance in a neutron-rich ??He nucleus.

The findings were published in Nature Communications under the title "Identification of a universal three-body s-wave resonance in ??He." This work fills a critical gap in the study of universal few-body phenomena in nuclear physics and opens a new avenue for research into strongly correlated quantum few-body systems.

Universality in physics describes the emergence of common features in vastly different systems. One fascinating example is the Efimov phenomenon where three-body resonantly interacting systems display universal properties. Efimov states have been observed in ultra-cold-atom systems, but their manifestation in nuclei remains elusive due to the long-range repulsive Coulomb interaction and the stringent requirement for at least two s-wave resonances in its subsystems. Recent theories propose another universality in three-body halos with only one s-wave resonance.

In the research, the authors report the identification of a precursor of this phenomenon in a neutron-rich ??He nucleus. With higher statistics and better sensitivities than previous experiments, they identify two low-lying 0⁺ states of ??He at ~ 1 MeV and ~ 2 MeV above its two-neutron decay threshold, and determine an s-wave scattering length of ~ ? 3.5 fm between ?He and neutron. It is revealed that the lower energy state, the ground state of ??He, is a three-body state with only s-wave interactions among its subsystems. This state manifests as a resonance structure, which is a direct consequence of a universal long-range three-body repulsion. The work sheds new light on quantum halos with finite lifetimes, providing a path toward their unified understanding across various scales and fields.

Figure 1. Three-body s-wave resonance structure of ??He

Sun Yelei is the first author and corresponding author of the paper. The collaboration includes 22 universities and research institutions worldwide, among which are the Technische Universit?t Darmstadt (Germany), Université Paris-Saclay (France), RIKEN Nishina Center (Japan), the University of Tokyo (Japan), Tokuyama University (Japan), the University of Electro-Communications (Japan), and the Universidad de Sevilla (Spain).

The work was supported by the National Natural Science Foundation of China, the Fundamental Research Funds for the Central Universities, and other grants.

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Editor: Lyu Xingyun