Effect of ΛΣ conversion on the Λ-particle binding in nuclear matter

The binding energy B of a Λ-particle in infinite nuclear matter is calculated in the so-called two-channel formalism (TCF), which explicitly takes account of the ΛΣ conversion, as well as in the more conventional one-channel formalism. In both calculations we assume phenomenological separable potentials of Yamaguchi's type which permit exact solutions of the Bethe-Goldstone equation. All the potentials are assumed to be central and are set up so that the low-energy Λp scattering data are fitted. In the TCF, data on the elastic and inelastic Σ − p cross sections are also considered. It is found that B in the TCF can be substantially smaller than in the OCF. The uncertainty in our result stems from the experimental data on the Σ − p reaction, which is of crucial importance in determining the TCF potentials. The difference of the values of B in the two formalisms is due to the Pauli principle which suppresses the ΛΣ conversion in nuclear matter. The relation between this effect in the TCF and three-body ΛNN forces in the OCF is clarified.