# Is the structure of 42Si understood?

## TL;DR

This study tests nuclear force models in 2Si by comparing experimental reaction data with shell-model predictions, revealing better agreement with the SDPF-MU interaction and insights into shape coexistence and excited states.

## Contribution

It provides a detailed experimental validation of shell-model interactions in 2Si, especially distinguishing between SDPF-MU and SDPF-U-Si models.

## Key findings

- Better agreement of data with SDPF-MU predictions
- Identification of a 2Si state as the second 0+ level
- Insights into shape coexistence in 2Si

## Abstract

A more detailed test of the implementation of nuclear forces that drive shell evolution in the pivotal nucleus \nuc{42}{Si} -- going beyond earlier comparisons of excited-state energies -- is important. The two leading shell-model effective interactions, SDPF-MU and SDPF-U-Si, both of which reproduce the low-lying \nuc{42}{Si}($2^+_1$) energy, but whose predictions for other observables differ significantly, are interrogated by the population of states in neutron-rich \nuc{42}{Si} with a one-proton removal reaction from \nuc{43}{P} projectiles at 81~MeV/nucleon. The measured cross sections to the individual \nuc{42}{Si} final states are compared to calculations that combine eikonal reaction dynamics with these shell-model nuclear structure overlaps. The differences in the two shell-model descriptions are examined and linked to predicted low-lying excited $0^+$ states and shape coexistence. Based on the present data, which are in better agreement with the SDPF-MU calculations, the state observed at 2150(13)~keV in \nuc{42}{Si} is proposed to be the ($0^+_2$) level.