Shell model calculation of Λ-hypernuclear spectra from (π⁺, K⁺)-reactions

Shell model calculations of Λ-hypernuclear spectra from (π⁺, K⁺)-experiments are presented and comparison is made with the recent data taken at Brookhaven. The reaction is described in a DWIA framework where the distortions are treated in a simplified eikonal approximation. The continuum part of the spectra is calculated with realistic Λ-wave functions and added to the bound-state spectrum. Using potential parameters extracted from earlier (K^-, π^-)-data on¹²C and¹⁶O our calculations agree very well with the experiments without any additional parameter. Fair agreement is reached even for heavier nuclei once the treatment of distortion effects is improved. Due to the more complicated neutron hole structure in heavier Λ-hypernuclei, deeply bound S _1/2 states appear as separate peaks only for nuclei up to²⁸Si. Possible improvements of our model are discussed qualitatively. We comment also on the question of partial quark deconfinement of the Λ-hyperon inside the hypernucleus.