Neutron single-particle strength in silicon isotopes: Constraining the driving forces of shell evolution

TL;DR

This study investigates shell evolution in neutron-rich silicon isotopes by analyzing neutron single-particle strengths from knockout reactions, revealing the influence of tensor forces and three-nucleon interactions on nuclear structure.

Contribution

It provides the first quantitative experimental evidence for the role of tensor forces and three-nucleon interactions in shell evolution of silicon isotopes.

Findings

Tensor force influences structure of 40 Si with N=26.

Cross-shell excitations support repulsive three-nucleon force contributions.

Neutron single-particle strengths measured in silicon isotopes.

Abstract

Shell evolution is studied in the neutron-rich silicon isotopes 36,38,40 Si using neutron single-particle strengths deduced from one-neutron knockout reactions. Configurations involving neutron excita- tions across the N = 20 and N = 28 shell gaps are quantified experimentally in these rare isotopes. Comparisons with shell model calculations show that the tensor force, understood to drive the col- lective behavior in 42 Si with N = 28, is already important in determining the structure of 40 Si with N = 26. New data relating to cross-shell excitations provide the first quantitative support for repulsive contributions to the cross-shell T = 1 interaction arising from three-nucleon forces.