Effect of a $\Lambda$ impurity in doubly magic nuclei

Abstract

We study the effect of a $\Lambda$ hyperon immersed in the doubly magic nuclei, ${}^{16}$O, ${}^{40}$Ca, ${}^{48}$Ca, and ${}^{208}$Pb, as well as the neutron magic nucleus ${}^{90}$Zr. For a $\Lambda$ in the $1s$ and $1p$ states in ${}_{\Lambda }^{17}$O, ${}_{\Lambda }^{41}$Ca, ${}_{\Lambda }^{49}$Ca, ${}_{\Lambda }^{91}$Zr, and ${}_{\Lambda }^{209}$Pb, we compare the single-particle energies and density distributions of the core nucleons with those of the nuclei without the $\Lambda$, as well as the point proton and neutron radii. A remarkable finding is that the bound $\Lambda$ induces a significant asymmetry in the proton-neutron density distributions in the core nucleus. This in turn gives rise to an appreciable, iso-vector mean field. As a consequence, the neutrons in the core are more attracted to the center of the nucleus, while the protons are pushed away, in comparison with those in the corresponding nucleus without the $\Lambda$.

Comments: This paper has been withdrawn by the authors due to errors in results