Spectroscopy of the neutron-rich hypernucleusHeΛ7from electron scattering

The missing mass spectroscopy of the $_{\mathrm{\ensuremath{\Lambda}}}^{7}\mathrm{He}$ hypernucleus was performed using the $^{7}\mathrm{Li}(e,{e}^{\ensuremath{'}}{K}^{+})\phantom{\rule{0.16em}{0ex}}_{\mathrm{\ensuremath{\Lambda}}}^{7}\mathrm{He}$ reaction at the Thomas Jefferson National Accelerator Facility Hall C. The $\mathrm{\ensuremath{\Lambda}}$-binding energy of the ground-state ($1/{2}^{+}$) was determined with a smaller error than that of the previous measurement, being ${B}_{\mathrm{\ensuremath{\Lambda}}}=5.55\ifmmode\pm\else\textpm\fi{}0.{10}^{\mathrm{stat}.}\ifmmode\pm\else\textpm\fi{}0.{11}^{\mathrm{sys}.}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. The experiment also provided new insight into charge symmetry breaking in $p$-shell hypernuclear systems. Finally, a peak at ${B}_{\mathrm{\ensuremath{\Lambda}}}=3.65\ifmmode\pm\else\textpm\fi{}0.{20}^{\mathrm{stat}.}\ifmmode\pm\else\textpm\fi{}0.{11}^{\mathrm{sys}.}\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ was observed and assigned as a mixture of $3/{2}^{+}$ and $5/{2}^{+}$ states, confirming the ``gluelike'' behavior of $\mathrm{\ensuremath{\Lambda}}$, which makes an unstable state in $^{6}\mathrm{He}$ stable against neutron emission.