Λ-Nucleon Interactions at Low and Intermediate Energies

The low-energy $\Lambda$-nucleon interaction has been represented by several effective central potentials which have a hard core of radius 0.4 F and four-parameter attractive wells with an interaction for large separations suggested by the two-pion-exchange mechanism. These potentials, which are consistent with the binding-energy data for the light hypernuclei, were taken to represent the $\Lambda$-nucleon interaction in even-parity states for energies greater than those which play a role in the binding of the light hypernuclei. These potentials and others of reduced strength were taken to represent the interaction in odd-parity states. The binding energy $D$ of a $\Lambda$ particle in nuclear matter and $\Lambda$-nucleon scattering cross sections were calculated with these potentials. The calculated cross sections and empirical cross sections for energies less than 76 MeV in the zero-momentum frame are in agreement only if the interaction in odd-parity states is taken to be (approximately) as strong as that in even-parity states. These effective central potentials of equal strength in even-parity and odd-parity states lead to values of $D$ close to 40 MeV.