Is the structure of ⁴²Si understood?

A more detailed test of the implementation of nuclear forces that drive shell evolution in the pivotal nucleus 42Si – 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 42Si(2+ 1) energy, but whose predictions for other observables differ significantly, are interrogated by the population of states in neutron-rich 42Si with a one-proton removal reaction from 43P projectiles at 81 MeV/nucleon. The measured cross sections to the individual 42Si 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 42Si is proposed to be the (0+ 2) level