Soft-core hyperon-nucleon potentials

A new Nijmegen soft-core OBE potential model is presented for the low-energy YN interactions. Besides the results for the fit to the scattering data, which largely defines the model, we also present some applications to hypernuclear systems using the G-matrix method. The potentials are generated by the exchange of nonets of pseudoscalar, vector, and scalar mesons. As is standard in the Nijmegen soft-core models, we also include the J=0 contributions from the tensor f₂,f₂^′,a₂, and pomeron Regge trajectories, and use Gaussian form factors to guarantee that the potentials have a soft behavior near the origin. An important innovation with respect to the original soft-core potential is the assignment of the cutoff masses for the baryon-baryon-meson (BBM) vertices in accordance with broken SU(3)_F, which serves to connect the NN and the YN channels. As a novel feature, we allow for medium strong breaking of the coupling constants, using the ³P₀ model with a Gell-Mann–Okubo hypercharge breaking for the BBM coupling. Charge-symmetry breaking in the Λp and Λn channels is included as well. We present six hyperon-nucleon potentials which describe the available YN cross section data equally well, but which exhibit some differences on a more detailed level. The differences are constructed such that the models encompass a range of scattering lengths in the ΣN and ΛN channels. In all cases, we obtained χ²/N_data≈0.55 for 35 YN data. In particular, we were able to fit the precise experimental datum r_R=0.468±0.010 for the inelastic capture ratio at rest. For the scalar-meson mixing angle we obtained values θ_S=37°–40°, which points to almost ideal mixing angles for the scalar qq̅ states. The G-matrix results indicate that the remarkably different spin-spin terms of the six potentials appear specifically in the energy spectra of Λ hypernuclei.