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 (N N ), hyperon-nucleon (Y N ), and hyperon-hyperon/nucleon (Y Y /Ξ N ) interactions in a unified way using broken SU(3) symmetry. SU(3) symmetry serves to connect the N N with the Y N and the Y Y 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 N N 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 ɛ 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 N N and Y N channels has been performed. The meson-baryon coupling constants are calculated via SU(3) using the coupling constants of the N N ⊕Y N 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 N N and Y N many parameters are essentially fixed by the N N data. A few, but severely constrained parameters, e.g., F /(F +D ) ratios, are left for determination of the Y N interactions and the Y Y experimental indications. The simultaneous fit of the ESC models to the N N - and Y N -scattering data with a single set of parameters has achieved excellent results for the N N and Y N data, and for the Y Y data in accordance with the experimental indications for Λ Λ and Ξ N . In the case of ESC16, the version discussed here, the achievements are: (i) For the selected 4313 p p and n p scattering data with energies 0 ≤Tlab≤350 MeV , the model reaches a fit having χ2/Ndata=1.10 . (ii) The deuteron binding energy and all the N N scattering lengths are fitted very nicely. (iii) The Y N data are described very well with χ2/Ndata=1.04 , giving at the same time a description of the Ξ N cross sections in agreement with the experimental indications. Conclusions: The ESC approach leads to an excellent description of the N N and Y N data, and for the scarce Y Y 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 P30-dominated quark-antiquark pair creation (QPC) model. The information about estimates of (i) the Λ - and Σ -nuclear well-depth, and (ii) the Λ Λ hypernuclei played an important role in the form of using constraints. In particular, the experimental indications for the Λ Λ -attraction and the Σ -nuclear well-depth were directive.- Publication:
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Physical Review C
- Pub Date:
- April 2019
- DOI:
- 10.1103/PhysRevC.99.044002
- Bibcode:
- 2019PhRvC..99d4002N