Particles, Astrophysics, and Nuclear Physics Seminar

The response of the core nucleus to the lambda in a hypernucleus is studied with a local density approximation, which reproduces quite well the energies and radii of the core nuclei as well as the lambda-single particle energies. The polarizing effect of the lambda depends on the core response through an "effective" compression modulus KA of the nucleus. For a certain class of energy functionals, KA is found to be almost independent of the compression modulus K of the infinite nuclear matter. This indeed is a surprising result, and differs from the Hartree-Fock calculations with effective interactions.

Reasons for this discrepancy are carefully examined. We consider valuesof K in the range of 100-400 MeV. Furthermore, the polarizing effects also depend critically on D, the lambda binding in nuclear matter at density. For only a direct lambda-N force: D and the core nucleus contracts giving rise to relatively larger core polarization. However, for a “saturating” D, which is required to fit the s.p. data, the s-shell hypernuclei binding energies and the low energy lambda-p scattering data, which results from a lambda-N force (including exchange) there may be a description of the nucleus with nucleons flowing from the interior to the surface. This is shown to reduce the core polarization effects substantially. The resulting changes in root mean square radius and core energy depend on A, but are mostly very small, justifying their general neglect.