Λ spin–orbit splitting in heavy hypernuclei as deduced from DWIA analyses of the reaction

By taking nuclear core excitations into account, detailed structure calculations of 89 ΛY have been performed as a function of the Λ spin–orbit splitting. The obtained wave functions have been used to estimate the (π+,K+) reaction cross sections within the distorted-wave impulse approximation (DWIA). A theoretical explanation is given quantitatively for the first time of how to understand the doublet substructure of each major peak observed in medium-heavy hypernuclear production. A small Λ spin–orbit splitting of around δ(0fΛ)=0.2 MeV is deduced, a value consistent with the small ΛN two-body spin–orbit interactions deduced from γ-ray measurements in three light hypernuclei.