Impurity effect of Lambda particle on the structure of 18F and 19F_Lambda

Abstract

We perform three-body model calculations for a $sd$-shell hypernucleus ${}_{\Lambda }^{19}$F (${}_{\Lambda }^{17}\mathrm{O}+p+n$) and its core nucleus ${}^{18}$F (${}^{16}\mathrm{O}+p+n$), employing a density-dependent contact interaction between the valence proton and neutron. We find that the $B(E2)$ value from the first excited state (with spin and parity of $I^{\pi }=3^{+}$) to the ground state ($I^{\pi }=1^{+}$) is slightly decreased by the addition of a $\Lambda$ particle, which exhibits the so called shrinkage effect of $\Lambda$ particle. We also show that the excitation energy of the $3^{+}$ state is reduced in ${}_{\Lambda }^{19}$F compared to ${}^{18}$F, as is observed in a $p$-shell nucleus ${}^6$Li. We discuss the mechanism of this reduction of the excitation energy, pointing out that it is caused by a different mechanism from that in ${}_{\Lambda }^7$Li.

Comments: 8 pages, 3 figures