Four-body correlations in light nuclei: (I). First excited 0 + states in 16O and 40Ca

Abstract

A new theory of treating the four-particle-four-hole excitations (with the ground-state correlations) in light, closed-shell nuclei is proposed by using the basic idea of a “two-step method” proposed by Eichler and Marumori. In the theory, four-body scattering correlations are taken up in the first step as the most important correlations in light nuclei, and the corresponding four-body scattering eigenmodes are constructed in the framework of the new Tamm-Dancoff approximation. The interaction between these eigenmodes are treated as the next step. Thus the four-particle-four-hole excitations in light, closed-shell nuclei are described by “phonons” composed of a correlated pair of the four-particle scattering eigenmode and the four-hole one. Here in part I, properties of the four body scattering eigenmodes are investigated in detail, and a close connection between the four-body scattering correlations and the α-cluster is clarified. As a result of the theory, it can be shown that the first excited 0 + states in 16O and 40Ca are mainly composed of the four-particle-four-hole excitations in the new Tamm-Dancoff sense. Essential ingredients to produce intrinsic deformations in the 0 + states are discussed.