Prediction of deformed halo nuclei $^{43,45}$Si from multiple criteria based on structure and reaction analyses

TL;DR

This work investigates the potential for deformed neutron halos in silicon isotopes by coupling the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the Glauber model to connect internal structure to reaction dynamics. It demonstrates that silicon isotopes near the neutron drip line, particularly $^{43}$Si and $^{45}$Si, exhibit weakly bound, predominantly $p$-wave neutrons forming halos that decouple from a deformed core, supported by extended density tails and single-particle analyses. Global halo criteria and orbital decompositions consistently indicate halo formation, while reaction observables such as enhanced cross sections and narrow longitudinal momentum distributions further corroborate the halo interpretation. The findings are robust across multiple density functionals and pairing schemes, suggesting that $^{43,45}$Si may become the heaviest known halo nuclei, with implications for future experiments in neutron-rich, mid-mass systems.

Abstract

Possible deformed neutron halos in silicon isotopes are investigated from both structure and reaction perspectives using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) combined with the Glauber model. The experimental neutron separation energies of silicon isotopes are well reproduced by the DRHBc theory. Multiple halo criteria are examined, including the global ones based on root-mean-square radii and density profiles, as well as the microscopic ones based on single-particle orbitals and their spatial distributions. Calculations employing different density functionals and pairing strengths consistently indicate the emergence of $p$-wave neutron halos in $^{43,45}$Si, accompanied by pronounced shape decoupling between the halo and the core. Moreover, the enhanced reaction cross sections and the narrow longitudinal momentum distributions of one-neutron removal residues provide additional evidence supporting the halo structures in $^{43,45}$Si.

Figures (7)

• Figure 1: One-neutron separation energy $S_{1n}$ as a function of neutron number $N$ in the DRHBc calculations with PC-PK1 for silicon isotopes, in comparison with the experimental data from AME2020 Wang2021CPC. The inset shows the $S_{1n}$ values obtained from DRHBc calculations with different density functionals, including PC-PK1, PC-L3R, NL3* and NL-SH, for silicon isotopes with $27 \leqslant N \leqslant 34$.
• Figure 2: Angle averaged neutron density distribution for $^{40-48}$Si in the DRHBc calculations with PC-PK1.
• Figure 3: (a) One-neutron halo scale $S_{\text{halo-1n}}$ and (b) halo parameter $N_{\text{halo}}$ for Si isotopes as functions of neutron number $N$ in the DRHBc calculations. See text for details.
• Figure 4: Single-neutron levels around the continuum threshold in the canonical basis for $^{43}$Si (a) and $^{45}$Si (b) versus the occupation probability $v^2$ in the DRHBc calculations. The levels are labeled by the quantum numbers $m^\pi$, and the main components in the DWS basis are given for the levels above $-6$ MeV. The Fermi energy $\lambda_n$ is shown by a dotted line.
• Figure 5: Neutron density distributions with $z$-axis as the symmetry axis for $^{43}$Si [(a)-(c)] and $^{45}$Si [(d)-(f)]. Here, (a) and (d) show the total densities; (b) and (e) show the core densities; (c) and (f) show the halo densities. In each plot, a dotted circle is drawn to guide the eye.