Gamow shell model predictions for six-proton unbound nucleus 20Si

Proton-rich nuclei beyond the proton drip line are of great interest in nuclear structure physics, due to exotic phenomena such as proton emissions and the Thomas-Ehrman shift (TES). In this work, we employ the Gamow shell model (GSM) to investigate the structure and decay of 20 Si, a candidate for six-proton (6 p ) emission, which can be produced via two-neutron knockout from the drip line nucleus 22 Si. We predict that its ground state decays via 6 p emission to the ground state of 14 O, with a decay energy E 6 p = 10.125 MeV and a width of 371 keV. A 2 + state is predicted at 1.7 MeV, comparable with that in 18 Mg, indicating the disappearance of the Z = 14 magic number in 20 Si. Instead, analyses of the many-body configurations and the average occupancies of the mirror states suggest the presence of dynamic TES in low-lying states of 19 Al/ 19 C and 20 Si/ 20 C. Further evidence is provided by analyzing the contributions of different components of the GSM Hamiltonian. Moreover, this study offers the first theoretical description of 20 Si and guidance for future experiments.