Spectroscopy of the neutron-rich hypernucleus $^{7}_{\Lambda}$He from electron scattering

TL;DR

This study used electron scattering to perform missing mass spectroscopy on the neutron-rich hypernucleus $^{7}_{\Lambda}$He, accurately measuring the $\Lambda$ binding energy and exploring charge symmetry breaking and the stabilizing effect of $\Lambda$ in hypernuclear systems.

Contribution

The paper provides a more precise measurement of the $\Lambda$ binding energy in $^{7}_{\Lambda}$He and offers new insights into charge symmetry breaking and the stabilizing 'gluelike' role of $\Lambda$ in hypernuclei.

Findings

Measured $\Lambda$ binding energy as 5.55 MeV with reduced error.

Observed a state at 3.65 MeV indicating mixed spin states.

Confirmed the stabilizing 'gluelike' effect of $\Lambda$ in hypernuclear systems.

Abstract

The missing mass spectroscopy of the $^{7}_{\Lambda}$He hypernucleus was performed, using the $^{7}$Li$(e,e^{\prime}K^{+})^{7}_{\Lambda}$He reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $\Lambda$ binding energy of the ground state (1/2$^{+}$) was determined with a smaller error than that of the previous measurement, being $B_{\Lambda}$ = 5.55 $\pm$ 0.10(stat.) $\pm$ 0.11(sys.) MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at $B_{\Lambda}$ = 3.65 $\pm$ 0.20(stat.) $\pm$ 0.11(sys.) MeV was observed and assigned as a mixture of 3/2$^{+}$ and 5/2$^{+}$ states, confirming the "gluelike" behavior of $\Lambda$, which makes an unstable state in $^{6}$He stable against neutron emission.