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

Abstract

The missing mass spectroscopy of the ${}_{\Lambda }^7$He hypernucleus was performed, using the ${}^7$Li$(e,e^{\prime }{K}^{+}{)}_{\Lambda }^7$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.

Comments: 6 pages, 4 figures