Spectroscopy of Lambda-9Li by 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 Be-9(e, e' K+) Li-9(Lambda) reaction. Method: Electroproduction of the hypernucleus Li-9(Lambda) has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a Be-9 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 Li-9(Lambda) 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 Lambda separation energy, B-Lambda, of 8.36 +/- 0.08 (stat.) +/- 0.08 (syst.) MeV was measured, in agreement with an earlier experiment.