Microscopic analysis of completeZr90(p,n) spectra including theΔisobar effect

A microscopic analysis of the complete forward angle spectra of the ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$(p,n) reaction is presented for an incident energy of 200 MeV. It is shown that the whole spectra up to an excitation energy of $E_x$=70 MeV are the result of correlated one-particle–one-hole (1p1h) spin-isospin transitions only. The spectra reflect, therefore, the linear spin-isospin response of the target nucleus to the probing (p,n) field. Two different cross section calculations are performed: one with usual random phase approximation wave functions and one with generalized random phase approximation wave functions which include Δ isobar degrees of freedom explicitly. We find that the theoretical cross sections calculated with random phase approximation wave functions, which provide the lower limit of spin-isospin strength, describe the data rather well at all scattering angles, while the random phase approximation +Δ cross sections underestimate the data at forward angles. In this connection we discuss the quenching of the spin-isospin strength in detail.