Four-body correlations in nuclei

TL;DR

This paper demonstrates that four-body correlated structures, or quartets, effectively describe low-energy spectra of 4n nuclei, highlighting the significance of four-body degrees of freedom beyond traditional models.

Contribution

It introduces a quartet-based formalism for describing 4n nuclei spectra, extending the approach to nuclei outside the sd shell and emphasizing the importance of four-body correlations.

Findings

Spectra of $^{24}$Mg and $^{28}$Si are well reproduced with $T$=0 quartets.

The $J$=0 quartet dominates the ground state structure.

The formalism successfully describes the low-lying spectrum of $^{92}$Pd.

Abstract

Low-energy spectra of 4$n$ nuclei are described with high accuracy in terms of four-body correlated structures ("quartets"). The states of all $N\geq Z$ nuclei belonging to the $A=24$ isobaric chain are represented as a superposition of two-quartet states, with quartets being characterized by isospin $T$ and angular momentum $J$. These quartets are assumed to be those describing the lowest states in $^{20}$Ne ($T_z$=0), $^{20}$F ($T_z$=1) and $^{20}$O ($T_z$=2). We find that the spectrum of the self-conjugate nucleus $^{24}$Mg can be well reproduced in terms of $T$=0 quartets only and that, among these, the $J$=0 quartet plays by far the leading role in the structure of the ground state. The same conclusion is drawn in the case of the three-quartet $N=Z$ nucleus $^{28}$Si. As an application of the quartet formalism to nuclei not confined to the $sd$ shell, we provide a description of the low-lying spectrum of the proton-rich $^{92}$Pd. The results achieved indicate that, in 4$n$ nuclei, four-body degrees of freedom are more important and more general than usually expected.