4He possesses a second 0+ state; the transition form factor has been measured via inelastic electron scattering. The nature of the 02+ state's spatial structure has been controversial. An accurate four-nucleon calculation utilizing a realistic NN force (Argonne V8′) plus phenomenological NNN three-body force has been performed for both the 4He ground state and second 0+ state (E x = 20.21 MeV) using the Gaussian expansion method. The calculated one-body densities and transition density show a significant difference between the states. The resulting impulse approximation transition form factor 4He(e,e′) He(02+) agrees with the available data. The overlap of the 02+ wave function with the trinucleon ground state suggests that the structure is primarily a loosely bound 3N+N system and not a breathing mode. It is found that a major part of the energy-weighted E0 sum rule value is exhausted by nonresonant, low-energy continuum states other than the second 0+ state, in contrast to heavier nuclei where a dominant fraction of the sum-rule limit is exhausted by the second 0+ state because it corresponds to a collective, breathing mode.
ASJC Scopus subject areas
- Nuclear and High Energy Physics