Intertwined effects of pairing and deformation on neutron halos in magnesium isotopes

TL;DR

This study uses self-consistent calculations to explore how pairing and deformation influence neutron halos in magnesium isotopes, revealing a new unpaired-particle haloing mechanism and predicting peanut-shaped halos.

Contribution

It introduces the concept of unpaired-particle haloing, showing how pairing enhances halos in odd-N nuclei, and demonstrates the intertwined effects of pairing and deformation on neutron halos.

Findings

Neutron halos are enhanced in odd-N magnesium isotopes due to unpaired-particle effects.

The halo in $^{37}$Mg has a peanut shape reflecting p-wave contributions.

The N-dependence of deformation significantly affects single-particle levels and halo formation.

Abstract

Matter radii of the $^{34-40}$Mg nuclei are investigated by self-consistent Hartree-Fock-Bogolyubov calculations assuming the axial symmetry. With the semi-realistic M3Y-P6 interaction, the $N$-dependence of the matter radii observed in the experiments is reproduced excellently. Both the pairing and the deformation play significant roles in an intertwined manner. The $^{35}$Mg nucleus has a smaller radius than the neighboring even-$N$ nuclei, which is attributed to its smaller deformation. In contrast, a neutron halo is obtained in $^{37}$Mg. We point out that, in contrast to the pairing anti-halo effect that may operate on the even-$N$ nuclei, the pair correlation enhances halos in odd-$N$ nuclei, owing to the new mechanism which we call \textit{unpaired-particle haloing}. The halo in $^{37}$Mg is predicted to have peanut shape in its intrinsic state, reflecting $p$-wave contribution, as in $^{40}$Mg. The $N$-dependence of the deformation is significant again, by which the single-particle level dominated by the $p$-wave component comes down.