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

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.

6 pages, 4 figures, accepted in Phys. Rev. Lett

References in corpus (12)

• Shell Model in the Complex Energy Plane
• A high-precision variational approach to three- and four-nucleon bound and zero-energy scattering states
• Ab initio four-body calculation of n-3He, p-3H, and d-d scattering
• Four-body calculation of proton-3He scattering
• Inversion doublets of 3N+N cluster structure in excited states of ${}^4$He
• Convenient location of a near-threshold proton-emitting resonance in ${}^{11}$B
• Description of Four- and Five-Nucleon Systems by Solving Faddeev-Yakubovsky Equations in Configuration Space
• Resonances of $A=4$ $T=1$ isospin triplet states within the \textit{ab initio} no-core Gamow shell model
• Probing the Non-exponential Decay Regime in Open Quantum Systems
• Is the first excited state of the $\alpha$-particle a breathing mode?
• Possible interpretation of the complex expectation values associated with resonances
• Ab initio framework for nuclear scattering and reactions induced by light projectiles