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

TL;DR

This study used the $(e,e^{ extprime}K^{+})$ reaction at Jefferson Lab to perform missing mass spectroscopy on the neutron-rich hypernucleus $^{9}_{ m \Lambda}Li$, revealing its ground state energy and excited states, and comparing results with shell model predictions.

Contribution

First measurement of the energy levels of $^{9}_{ m \Lambda}Li$ using the $(e,e^{ extprime}K^{+})$ reaction, providing new data on hypernuclear structure and cluster configurations.

Findings

Ground state energy $B_{ m \\Lambda}^{ m g.s.}=8.84 \\pm 0.17^{\\rm stat.} \\pm 0.15^{\\rm sys.}~\text{MeV}

Observed excited states at $E_{\\Lambda}({\rm no.~2})=1.74 \\pm 0.27^{\\rm stat.} \\pm 0.11^{\\rm sys.}~\text{MeV}$ and $E_{\\Lambda}({\rm no.~3})=3.30 \\pm 0.24^{\\rm stat.} \\pm 0.11^{\\rm sys.}~\text{MeV}$

The $E_{\\Lambda}({\rm no.~3})$ state suggests a developed ${\rm ^{5}He}+t$ cluster structure.

Abstract

Missing mass spectroscopy with the $(e,e^{\prime}K^{+})$ reaction was performed at Jefferson Laboratory's Hall C for the neutron rich $\Lambda$ hypernucleus $^{9}_{\Lambda}{\rm Li}$. The ground state energy was obtained to be $B_{\Lambda}^{\rm g.s.}=8.84\pm0.17^{\rm stat.}\pm0.15^{\rm sys.}~{\rm MeV}$ 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 $E_{\Lambda}({\rm no.~2})=1.74\pm0.27^{\rm stat.}\pm0.11^{\rm sys.}~{\rm MeV}$ and $E_{\Lambda}({\rm no.~3})=3.30\pm0.24^{\rm stat.}\pm0.11^{\rm sys.}~{\rm MeV}$, 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.