Single-Particle Spectral Function of the Λ Hyperon in Finite Nuclei

The spectral function of the Lambda hyperon in finite nuclei is calculated from the corresponding Lambda self-energy using different hyperon-nucleon interactions of the Julich and Nijmegen groups. Binding energies and disoccupation numbers of different single-particle states are obtained for various hypernuclei from He-5(Lambda) to Pb-209(Lambda). The discrete and the continuum contributions of the single-Lambda spectral function are computed. The Z-factor, that measures the importance of correlations, is also calculated. The results show that its value is relatively large, indicating that the Lambda hyperon is less correlated than nucleons in agreement with the results obtained by other authors for the correlations of the Lambda in infinite nuclear matter. The disoccupation numbers are obtained by integrating the spectral function over the energy. The results show that the discrete contribution to the disoccupation number decreases when increasing the momentum of the Lambda. This indicates that, in the production reactions of hypernuclei, the Lambda hyperon is mostly formed in a quasi-free state.