Giant spin-isospin vibrations and the continuum spectra from the (p,n) reaction at forward angles

Abstract

The giant Gamow-Teller (GT) resonance and the spin-isospin multipole vibrations are calculated in terms of the continuum RPA. The effective particle-hole interaction consists of the Migdal parameter g′ = 0.7 ( in units of ƒ; 2 μ π 2 ≈390 MeV · fm 3) and the one-pion exchange potential. The RPA response functions are obtained within the full 1p-1h space. In addition to the natural escaping width of the single particle, a constant spreading width for 1p-lh states is incorporated into the correlation function, which makes numerical calculations fast and feasible. The giant GT resonances in 90Zr and 208Pb collect, respectively, about 80% and 93% strengths of the sum-rule limit within the nucleon degrees of freedom. It is found that the strengths are further quenched by about 30% due to the coupling with the isobar Δ(1230)-hole configuration. The total quenching thus amounts to 0≈45% and ≈40% respectively in two cases, which is in fair agreement with experiment. The continuum cross section of the 90Zr(p, n) reaction at forward angles are calculated for spins up to J = 4 with both parities in the distorted-wave Born approximation. While the giant GT resonance is located at a low excitation energy h ̵ ω ≈ 17 MeV , the broad peaks of the dipole and quadrupole modes are found to dominate at h ̵ ω ≈ 25 and 35 MeV , respectively. The calculation fairly reproduces the experimental inclusive cross sections up to h ̵ ω ≈ 50 MeV .