Spectroscopy of LiΛ9 by electroproduction

Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei can provide information on the details of the effective hyperon-nucleon interaction. Purpose: To obtain a high-resolution spectrum for the 9Be(e,e'K+)9ΛLi reaction. Method: Electroproduction of the hypernucleus 9ΛLi has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a 9Be target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. Results: The cross section to low-lying states of 9ΛLi is concentrated within 3 MeV of the ground state and can be fitted 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. A Λ separation energy, BΛ, of 8.36±0.08 (stat.) ±0.08 (syst.) MeV was measured, in agreement with an earlier experiment.