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arXiv · 2306.05192

Description of the proton-decaying 0$^+_2$ resonance of the $\alpha$ particle

N. Michel·W. Nazarewicz·M. Płoszajczak
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Abstract

The recent precise experimental determination of the monopole transition form factor from the ground state of $^4$He to its $0^+_2$ resonance via electron scattering has reinvigorated discussions about the nature of this first excited state of the $\alpha$ particle. The $0^+_2$ state has been traditionally interpreted in the literature as the isoscalar monopole resonance (breathing mode) or, alternatively, as a particle-hole shell-model excitation. To better understand the nature of this state, which lies only $\sim$ 410 keV above the proton emission threshold, we employ the coupled-channel representation of the no-core Gamow shell model. By considering the $[^3$H$ + p]$, $[^3$He$ + n]$, and $[^2$H+$^2$H] reaction channels, we explain the excitation energy and monopole form-factor of the $0^+_2$ state. We argue that the continuum coupling strongly impacts the nature of this state, which carries characteristics of the proton decay threshold.

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N. Michel, W. Nazarewicz, M. Płoszajczak. 2023-06-08. Description of the proton-decaying 0$^+_2$ resonance of the $\alpha$ particle. https://arxiv.org/abs/2306.05192

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