The particle, also known as helium-4, consists of two protons and two neutrons. Although it is one of the most widely studied nuclei, the exact nature of its excited states remains unclear.
A recent experimental study of the first excited state of helium-4, labeled by scientists as 0+2, has sparked a new debate due to the large discrepancy between the experimental data and the theory**.
To better understand the nature of this state, Professor Nicholas Michel of the Institute of Modern Physics of the Chinese Academy of Sciences and his collaborators employed a nuclear-free Gamow shell model to study the 0+2 states of the resonant structure helium-4. The study was published in Physical Review Letters and was listed as a "Selected Physics" article.
The 0+2 state of helium-4 is unbound only at about 410 kEV. It is a single proton emitter, but it has a short lifespan. The 0+2 resonance is traditionally regarded as a particle-hole excitation of the respiration mode or the helium 4 ground state.
Michelle and his collaborators have provided a new description of the 0+2 states of helium-4. Their **0+2 resonance has a rather complex structure that exhibits strong continuous coupling between different decay channels.
It is found that the continuous coupling strongly influences the properties of this proton emission state, and the best agreement with the experimental data of the monopole shape factor is obtained at the experimental energy.
The researchers suggest that the 0+2 state should not be seen as a respiratory oscillation or particle-hole excitation, but rather, as a broad resonance of threshold alignment.
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