Folding model study of α-p scattering: Systematics of elastic scattering, effective interaction, and inelastic excitation of N* resonances
Abstract
For a description of elastic and inelastic α-p scattering exciting N* resonances optical potentials and transition potentials were derived by folding nucleon and nucleus mass densities with a variable range effective interaction. For elastic α-p scattering in forward direction, a reasonable description of essentially all data has been obtained from low energies up to the GeV region. Also, α scattering from 4He and 12C is quite well described with potentials, which indicate that the used folding method is a valid approach for the systems in question. The strong energy dependence of the deduced potentials can be accounted for by a sum of scalar and vector meson-exchange potentials and a soft Pomeron-exchange contribution. The scalar meson-exchange potential falls off rapidly with energy and has a large radius in agreement with theoretical predictions. Consistent with the flavor SU(3) quark model, the vector-meson coupling is rather weak in the central potential, but is strong in the spin-orbit potential, for which a soft Pomeron contribution is negligible. The differences between the deduced α-p and nucleon-nucleon (NN) potentials are understood; further, an excellent description of the energy dependence of the s-wave NN amplitudes is obtained in the folding model framework. Distorted wave Born approximation calculations for inelastic α-p scattering show a t-dependence of the L=0 cross section consistent with empirical form factors. Absolute yields for excitation of the resonances P11(1440), D13(1520) and F15(1680) were calculated, using resonance shapes from π-N scattering. A quantitative description of the data at Eα=4.2 GeV is obtained using fluid-dynamical transition densities and strengths exhausting large fractions of scalar energy weighted sum rules. The rather pure scalar (non-spin-isospin-flip) character of these excitations and the observed cross sections are in severe conflict with the constituent quark model. Finally, a prediction is made for p-α scattering at an incident energy of Ep=2.2 GeV, which yields strongly increased cross sections for N* excitations.
- Publication:
-
Physical Review C
- Pub Date:
- June 2003
- DOI:
- 10.1103/PhysRevC.67.064001
- Bibcode:
- 2003PhRvC..67f4001M
- Keywords:
-
- 25.55.Ci;
- 25.10.+s;
- 13.75.Cs;
- 14.20.Gk;
- Elastic and inelastic scattering;
- Nuclear reactions involving few-nucleon systems;
- Nucleon-nucleon interactions;
- Baryon resonances with S=0