Extended-soft-core baryon-baryon model ESC16. I. Nucleon-nucleon scattering

Abstract

Background: The Nijmegen extended-soft-core (ESC) model ESC16, as well as its predecessors ESC04-ESC08, describe the nucleon-nucleon (NN), hyperon-nucleon (YN), and hyperon-hyperon/nucleon (YY/ΞN) interactions in a unified way using broken SU(3) symmetry. SU(3) symmetry serves to connect the NN with the YN and the YY channels. In the spirit of the Yukawa approach to the nuclear force problem, the interactions are studied from the meson-exchange picture viewpoint, using generalized soft-core Yukawa functions. The meson exchanges are supplemented with diffractive contributions due to multiple-gluon exchanges. The extended-soft-core (ESC) meson-exchange interactions consist of local and nonlocal potentials due to (i) one-boson exchanges (OBE), which are the members of nonets of pseudoscalar, vector, scalar, and axial-vector mesons, (ii) diffractive exchanges, (iii) two-pseudoscalar exchange (PS-PS), and (iv) meson-pair exchange (MPE). The OBE and MPE vertices are regulated by Gaussian form factors producing potentials with a soft behavior near the origin. The assignment of the cutoff masses for the BBM vertices is dependent on the SU(3) classification of the exchanged mesons for OBE and a similar scheme for MPE.Purpose: The evolution of the ESC approach to the ESC16 model for the baryon-baryon (BB) interactions of the SU(3) flavor octet of baryons (N, Λ, Σ, and Ξ) is described and presented. In this first of a series of papers, the NN model and results are reported in detail. Methods: Important nonstandard ingredients in the OBE sector in the ESC models are (i) the axial-vector meson potentials, and (ii) a zero in the scalar- and axial-vector meson form factors. Furthermore, the strange scalar κ meson is treated within the scheme of the Gell-Mann-Okubo mass relations, and like the ρ and ϵ treated as a broad meson. The multiple-gluon exchanges are elaborated further by adding contributions due to odd number of gluon exchanges. A novel contribution is the incorporation of structural effects due to the quark core of the baryons. In establishing the parameters of the model a simultaneous fit to NN and YN channels has been performed. The meson-baryon coupling constants are calculated via SU(3) using the coupling constants of the NNYN analysis as input. In ESC16 the couplings are kept completely SU(3) symmetric. About 25 physical coupling parameters and 8 cutoff and diffractive masses were searched. Results: In the fit to NN and YN many parameters are essentially fixed by the NN data. A few, but severely constrained parameters, e.g., F/(F+D) ratios, are left for determination of the YN interactions and the YY experimental indications. The simultaneous fit of the ESC models to the NN- and YN-scattering data with a single set of parameters has achieved excellent results for the NN and YN data, and for the YY data in accordance with the experimental indications for ΛΛ and ΞN. In the case of ESC16, the version discussed here, the achievements are: (i) For the selected 4313 pp and np scattering data with energies 0≤Tlab≤350MeV, the model reaches a fit having χ2/Ndata=1.10. (ii) The deuteron binding energy and all the NN scattering lengths are fitted very nicely. (iii) The YN data are described very well with χ2/Ndata=1.04, giving at the same time a description of the ΞN cross sections in agreement with the experimental indications. Conclusions: The ESC approach leads to an excellent description of the NN and YN data, and for the scarce YY data. The added innovations as well as the treatment of mass broken SU(3) make it possible to keep the meson coupling parameters and the F/(F+D) ratios of the model qualitatively in accordance with the predictions of the P03-dominated quark-antiquark pair creation (QPC) model. The information about estimates of (i) the Λ- and Σ-nuclear well-depth, and (ii) the ΛΛ hypernuclei played an important role in the form of using constraints. In particular, the experimental indications for the ΛΛ-attraction and the Σ-nuclear well-depth were directive.