Spectroscopy ofLiΛ9by electroproduction

Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei provides information on the details of the effective hyperon-nucleon interaction.Purpose: To obtain a high-resolution binding-energy spectrum for the ${}^{9}\mathrm{Be}(e,{e}^{\ensuremath{'}}{K}^{+})_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ reaction.Method: Electroproduction of the hypernucleus $_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a $^{9}\mathrm{Be}$ target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a ring imaging Cherenkov detector were added to the Hall A standard equipment.Results: The cross section to low-lying states of $_{\ensuremath{\Lambda}}^{9}\mathrm{Li}$ is concentrated within 3 MeV of the ground state and can be fit with four peaks. The positions of the doublets agree with theory while a disagreement could exist with respect to the relative strengths of the peaks in the doublets. The $\ensuremath{\Lambda}$ separation energy, ${B}_{\ensuremath{\Lambda}}$, of $8.36\ifmmode\pm\else\textpm\fi{}0.08$ (stat.) $\ifmmode\pm\else\textpm\fi{}0.08$ (syst.) MeV was measured, in agreement with an earlier experiment.