Spectroscopy of A =9 hyperlithium with the (e ,e'K+) reaction

Missing mass spectroscopy with the (e ,e^'K⁺ ) reaction was performed at Jefferson Laboratory's Hall C for the neutron-rich Λ hypernucleus ^Li9_Λ. The ground-state (g.s.) energy was obtained to be B_Λ^{g .s .}=8.84 ±0 .17^{stat .}±0 .15^{sys .}MeV by using shell-model calculations of a cross-section ratio and an energy separation of the spin doublet states (3 /2₁⁺ and 5 /2₁⁺ ). In addition, peaks that are considered to be states of [⁸Li(3⁺) ⊗s_Λ=3 /2₂⁺,1 /2⁺] and [⁸Li(1⁺) ⊗s_Λ=5 /2₂⁺,7 /2⁺] were observed at E_Λ(no . 2 ) =1.74 ±0 .27^{stat .}±0 .11^{sys .} and E_Λ(no . 3 ) =3.30 ±0 .24^{stat .}±0 .11^{sys .}MeV , respectively. The E_Λ(no . 3 ) is larger than shell-model predictions by a few hundred keV, and the difference would indicate that a ⁵He+t structure is more developed for the 3⁺ state than those for the 2⁺ and 1⁺ states in a core nucleus ⁸Li as a cluster model calculation suggests.