Gamow-Teller strength in the continuum and quenching problem

Differential cross sections at θ_lab = 0.0° 12.3° and a complete set of polarization transfer observables at θ_lab = 0.0° are measured for the ⁹⁰Zr(p, n) reaction at T_p = 295 MeV. A multipole decomposition (MD) technique is applied to the cross sections to extract partial cross sections σ_L with L=0, 1, 2, and 3 contributions. A significant amount of σ_L=0 is found in the highly excited continuum region. After subtracting the estimated iso-vector spin-monopole strength from σ_L=0, the Gamow-Teller (GT) strength B(GT) is deduced to be S_β- = ∑ B(GT) = 28 ± 1.6 ± 5.4. The total spin transfer ∑(0°) which is independent of the nuclear reaction mechanisms such as the effective nncleon-nucleon interaction or distortions is derived from the complete set of polarization transfer observables. It is close to unity up to 50 MeV excitation indicating the strong spin-flip character of the continuum. By using the relation between the polarization transfer observables the fractions of natural-parity and unnatural-parity transitions are also obtained and the dominance of unnatural-parity transitions in the continuum is found. These results are consistent with those derived from the MD analysis. The S_β- - S_β+ value is 27.1 and this is 90% of Ikeda's sum rule value of 3(N - Z)=30. Consequently it is concluded that the quenching of the GT strength is small and the quenching mechanism due to the ΔN admixture seems to play a minor role.