$N=Z$ nuclei: A laboratory for neutron-proton collective mode

TL;DR

This paper explores neutron-proton pairing correlations in N=Z nuclei, examining evidence for different coupling schemes and their impact on nuclear phenomena, highlighting recent advances enabled by radioactive ion beam technology.

Contribution

It introduces new insights into neutron-proton pair coupling schemes, including spin-aligned and quartet couplings, in N=Z nuclei, expanding understanding of np correlations beyond traditional pairing models.

Findings

Evidence for np pair coupling from various perspectives

Analysis of np influence on Wigner effect and mass correlations

Explanation of spin-aligned and quartet coupling schemes

Abstract

The neutron-neutron and proton-proton pairing correlations have long been recognised to be the dominant many-body correlation beyond the nuclear mean field since the introduction of pairing mechanism by Bohr, Mottelson and Pines nearly 60 year ago. Nevertheless, few conclusion has been reached concerning the existence of analogous neutron-proton (np) pair correlated state. One can see a renaissance in np correlation studies in relation to the significant progress in radioactive ion beam facilities and detection techniques. The np pairs can couple isospin T = 1 (isovector) or 0 (isoscalar). In the isovector channel, the angular momentum zero component is expected to be the most importance one. On the other hand, as one may infer from the general properties of the np two-body interaction, in the isoscalar channel, both the np pairs with minimum (J=1) and maximum (J=2j) spin values can be important. In this contribution, we will discuss the possible evidence for np pair coupling from different perspective and analyze its influence on interesting phenomena including the Wigner effect and mass correlations in odd-odd nuclei. In particular, we will explain the spin-aligned pair coupling scheme and quartet coupling involving pairs with maximum (J=2j) spin values.