Modification of triaxial deformation and change of spectrum in $^{25}_{\ \Lambda}$Mg caused by $\Lambda$ hyperon

Abstract

The positive-parity states of $^{25}_{\ \Lambda}$Mg with a $\Lambda$ hyperon in $s$ orbit were studied with the antisymmetrized molecular dynamics for hypernuclei. We discuss two bands of $^{25}_{\ \Lambda}$Mg corresponding to the $K^\pi=0^+$ and $2^+$ bands of $^{24}$Mg. It is found that the energy of the $K^\pi = 2^+ \otimes \Lambda_s$ band is shifted up by about 200 keV compared to $^{24}$Mg. This is because the $\Lambda$ hyperon in $s$ orbit reduces the quadrupole deformation of the $K^\pi = 0^+ \otimes \Lambda_s$ band, while it does not change the deformation of the $K^\pi = 2^+ \otimes \Lambda_s$ band significantly.