Four-body calculation of the first excited state of 4He using a realistic NN interaction:: 4He(e,e′)4He(02+) and the monopole sum rule -: art. no. 031001

He-4 possesses a second 0(+) state; the transition form factor has been measured via inelastic electron scattering. The nature of the 0(2)(+) 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 He-4 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 He-4(e,e('))He-4(0(2)(+)) agrees with the available data. The overlap of the 0(2)(+) 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.