Study of quark degrees of freedom in nuclei by precise measurement of Gamow-Teller spin sum rule value

点击翻译按钮获取中文摘要

This research is intended to explore quantitatively the quark degrees of freedom in nuclei by extracting a quenching value of spin sum rule (Ikeda sum rule). For that we need to obtain the precise β^+ B(GT) value which can be accomplished through the (n,p) reaction at intermediate energy.This research was carried out in the following way.1. We have constructed the (n,p) facility at the Research Center for Nuclear Physics at Osaka University.2. The precise angular distributions for the cross sections and analyzing powers have been measured for ^<90>Zr(n,p) reaction at 300 MeV.3. The multipole decomposition analysis (MDA) has been applied to the ^<90>Zr(n,p) data and the reliable σ(ΔL = 0) distribution is extracted up to an excitation energy of 70 MeV.4. The σ(ΔL = 0) is used to get the B(β^+ GT) value. After integrating the B(β^+ GT) values in the continuum up to an appropriate excitation energy, the total B(β^+ GT) strength is obtained as S(β^+)=3.0 ± 0.4.5. By using the previously obtained S(β^-) value, the quenching value in terms of the spin sum rule (Ikeda sum rule) can be derived as:Q = [S(β^-) - S(β^+)]/3(N - Z) = 0.83 ±0.06.6. This Q value leads to the Landau-Migdal (LM) parameterg'_<NΔ> = 0.28-0.35.The smallness of g'_<NΔ> indicates the smallness of the Δ-hole state contribution. This implies that the quark degrees of freedom in nuclei is rather small. Present g'_<NΔ> value is obtained for the first time from the experiment. This project has been completed very smoothly with fruitful results.