Spectroscopy of $A=9$ hyperlithium by the $(e,e^{prime}K^{+})$ reaction

Missing mass spectroscopy with the $(e,e^{prime}K^{+})$ reaction was performed at Jefferson Laboratorys Hall C for the neutron rich $Lambda$ hypernucleus $^{9}_{Lambda}{rm Li}$. The ground state energy was obtained to be $B_{Lambda}^{rm g.s.}=8.84pm0.17^{rm stat.}pm0.15^{rm sys.}~{rm MeV}$ by using shell model calculations of a cross section ratio and an energy separation of the spin doublet states ($3/2^{+}_1$ and $5/2^{+}_1$). In addition, peaks that are considered to be states of [$^{8}{rm Li}(3^{+})otimes s_{Lambda}=3/2^{+}_{2}, 1/2^{+}$] and [$^{8}{rm Li}(1^{+})otimes s_{Lambda}=5/2^{+}_{2}, 7/2^{+}$] were observed at $E_{Lambda}({rm no.~2})=1.74pm0.27^{rm stat.}pm0.11^{rm sys.}~{rm MeV}$ and $E_{Lambda}({rm no.~3})=3.30pm0.24^{rm stat.}pm0.11^{rm sys.}~{rm MeV}$, respectively. The $E_{Lambda}({rm no.~3})$ is larger than shell model predictions by a few hundred keV, and the difference would indicate that a ${rm ^{5}He}+t$ structure is more developed for the $3^{+}$ state than those for the $2^{+}$ and $1^{+}$ states in a core nucleus $^{8}{rm Li}$ as a cluster model calculation suggests.