Λ single-particle energies

We are continuing our work on the Λ hyperon single-particle (s.p.) energies and their interpretation in terms of the basic Λ-nuclear interactions. In particular we are interpreting the results obtained by S.C. Pieper, A. Usmani and Q.N. Usmani. We obtain about 30 MeV for the repulsive contribution of the three-body ΛNN forces in nuclear matter. We are able to exclude purely open-quotes dispersiveclose quotes ΛNN forces. We are investigating the mix of dispersive and two-pion-exchange ΛNN forces which provide a fit to the s.p. data. For interactions, which provide a fit to the s.p. data, the Λ binding energy as a function of the nuclear matter density shows characteristic saturation features with a maximum at a density not very different from that of normal nuclear matter. We obtain a more precise measure of the space-exchange part of the Λ-nuclear force than was previously available, corresponding to an exchange parameter ≅ 0.32. The space-exchange force is rather directly related to the effective mass of a Λ in the nuclear medium and turns out to be about 70% of its free mass. As a result, we also obtain a much better value for the p-state Λ-nucleus potential which is about 40% of the s-state potential. The A binding to nuclear matter is determined to be ≅ 28 MeV