Neutron-proton pairing in the unstable N=Z nuclei of the f-shell through two-nucleon transfer reactions

TL;DR

This study investigates neutron-proton pairing in N=Z f-shell nuclei using two-nucleon transfer reactions, revealing a significant reduction in isoscalar pairing and potential superfluid behavior in the isovector channel.

Contribution

It provides experimental data and analysis on neutron-proton pairing in f-shell nuclei, highlighting the suppression of isoscalar pairing and the evolution of pairing correlations across the shell.

Findings

Very low cross-sections for J=1+, T=0 state in f-shell nuclei.

Significant reduction of isoscalar pairing compared to sd-shell.

Increase in isovector pairing towards mid-shell suggests superfluidity.

Abstract

Pair transfer is a unique tool to study pairing correlations in nuclei. Neutron-proton pairing is investigated in the N=Z nuclei of the f-shell, through the reaction (p,3He) in inverse kinematics, that allows to populate at the same time the lowest J=0+, T=1 (isovector pairing) state and J=1+, T=0 (isoscalar pairing) state. Radioactive beams of 56Ni and 52Fe produced by fragmentation at the GANIL/LISE facility combined with particle and gamma-ray detection make it possible to carry out this study from 48Cr (mid-shell nucleus) to 56Ni (doubly-magic nucleus). The cross-sections were extracted and compared with second-order distorted-wave born approximation (DWBA) calculations performed with neutron-proton amplitudes obtained from shell model calculations with GXPF1 interaction. Very low cross-sections for the J=1+,T=0 state (isoscalar channel) were observed. The cross-section for 56Ni is one of order of magnitude lower than for 40Ca showing a strong reduction of the isoscalar channel in the f-shell as compared to the sd-shell. On the other hand, the increase of the cross-section towards the middle of the shell for the isovector channel points towards a possible superfluid phase.