U. Straub

Hyperon-nucleon interaction in the quark cluster model☆

Abstract The lambda-nucleon and sigma-nucleon interaction is described in the nonrelativistic quark cluster model. The SU(3) flavor symmetry breaking due to the different quark masses is taken into account, i.e. different wavefunctions for the light (up, down) and heavy (strange) quarks are used in flavor and orbital space. The six-quark wavefunction is fully antisymmetrized. The model hamiltonian contains gluon exchange, pseudoscalar meson exchange and a phenomenological σ-meson exchange. The six-quark scattering problem is solved within the resonating group method. The experimental lambda-nucleon and sigma-nucleon cross sections are well reproduced.

Hyperon-nucleon interactions in a chiral SU(3) quark model☆

Quark-chiral field interaction is studied in terms of the linear realization of the Lagrangian which is invariant under the SU(3)(L) x SU(3)(R) infinitesimal transformation and then is applied to the hyperon-nucleon scattering calculation in the framework of RGM, It is shown that the SU(3) chiral scalar fields affect the spin dependence of the Lambda-N interaction and can improve the theoretical Sigma(-)p scattering cross section

Binding energy of the dihyperon in the quark cluster model

Abstract The dihyperon is described in the non-relativistic quark cluster model. The SU(3) flavor symmetry breaking due to the different quark masses is taken into account not only in the hamiltonian, but also in the quark wave functions. The interaction contains the one-gluon-exchange potential, pseudoscalar-meson exchange between quarks plus an additional phenomenological σ-meson exchange. The mass of the dihyperon is predicted to be (2211 ± 5) MeV, i.e. a binding energy of the dihyperon of (−20 ± 5) MeV below the ΛΛ threshold is found.

The Baryon baryon interaction in a modified quark model

Abstract The quark-cluster model with coupling constants constraint by chiral symmetry is extended to include strange quarks. In this model, besides the confinement and one-gluon exchange potentials, the pseudoscalar mesons and sigma (σ) meson exchanges are included as the nonperturbative effect. Using this interaction we studied the binding energy of the deuteron, the NN scattering phase shifts and the hyperon-nucleon cross sections in the framework of the resonating group method (RGM). The results are reasonably consistent with experiments.

Mesonic decay of 5ΛHe with quark-model-based hypernuclear wave function

Abstract We have evaluated the mesonic decay of the 5 Λ He hypernucleus by using a Λ wave function generated from the quark cluster model. As a consequence of the Λ N repulsion at short distances we obtain a Λ wave function in the nucleus with a large radius. The smaller overlap with the 4 He core with respect to simpler wave functions and the effect of the pion renormalization increase the mesonic width considerably and one obtains a good reproduction of the experimental data.

Hyperon-nucleon interaction and the H-dibaryon in the quark cluster model

Abstract The non-relativistic cluster model is used to describe the hyperon-nucleon (ΛN, ΣN) and hyperon-hyperon (H-dibaryon) interaction. Including central and tensor parts of the one-gluon exchange, pseudoscalar-meson exchange plus an additional phenomenological σ-meson exchange, a very good fit of the experimental hyperon-nucleon cross-sections is achieved. Applying this model to the H-dibaryon, a bound state with a binding energy of (−15 ± 5) MeV below the ΛΛ threshold is found, i.e. the mass of the H-dibaryon is predicted to be around 2216 MeV.

Lambda-nucleon scattering in the quark-cluster model☆

Abstract The lambda-nucleon scattering is calculated in the framework of the nonrelativistic quark-cluster model. The short-range interaction is described by quark and one-gluon exchange. This interaction gives typical hard-core S-wave phase shifts. The corresponding hard-core radius is by about 30 percent greater in the 1 S 0 state than in 3 S 1 . In order to get a realistic description of the interaction, a medium-range force caused by the exchange of a nonet of pseudoscalar mesons and a phenomenological σ-meson has in addition to the short-range interaction been taken into account. With this full potential the S-wave phase shifts and total elastic cross sections are calculated. The agreement with the measured low-energy total cross section is very good. The scattering lengths in the singlet state are smaller than in the triplet state.

Baryon-baryon interaction in the quark model and the H-dibaryon

Abstract The non-relativistic quark cluster model has been successfully used for describing the nucleon-nucleon interaction. Here it is extended to describe the hyperon-nucleon (ΛN, ΣN) and hyperon-hyperon (H-dibaryon) interaction. Including central and tensor parts of the one-gluon exchange, pseudoscalar-meson exchange plus an additional phenomenological σ-meson exchange, a very good fit of the experimental hyperon-nucleon cross-sections is achieved. Applying this model to the H-dibaryon, a bound state with a binding energy of (−15 ± 5) MeV below the ΛΛ threshold is found, i.e. the mass of the H-dibaryon is predicted to be around 2216 MeV.

Aspects of “scalar” versus “vector” confinement in qqq and 6q systems

Abstract A comparative study is made of scalar versus vector forms of confinement (both with quadratic shapes) to the extent they affect the properties of bound qqq(N, Δ) and NN(6q) scattering systems. The vector form (≈ γ μ (1) γ μ (2) ) exhibits some additional structure (Q r , J · S ) in the confinement potential which is sensitive to the N, Δ properties, but its effect on NN phase shifts is quite small. The scalar form, being free from this additional structure, does not show such sensitivity to either system. Both forms reproduce the observed S-wave phase shifts quite well.

The quark model and the spin observables for nucleon-nucleon scattering☆

Abstract Polarization observables for the nucleon-nucleon scattering are investigated in the framework of the non-relativistic constituent quark model below T lab = 250 MeV. The polarization observables obtained either from theoretically computed phase shifts or from experimental phase shifts are compared. In general the same polarization observable calculated from various experimental phase-shift analyses are not identical. The difference depends very much on the energy and the nucleon-nucleon system considered. The typical deviation to the the theoretically computed polarizations is roughly of the same order. This means a surprisingly good agreement is found. Furthermore, there are indications that some of the NN polarization observables are more sensitive to variations of small distance interaction parameters than the differential cross section or other simple polarization observables. An extended version of this paper including the full set of plots of all 25 polarization observables for four energies may be obtained upon request directly from the authors.