Gamow-Teller strength of90Nb in the continuum studied via multipole decomposition analysis of the90Zr(p,n)reaction at 295 MeV

The double differential cross sections at ${\theta }_{\mathrm{lab}}$ between $0.0°$ and $12.3°$ and the polarization transfer $D_{\mathrm{NN}}$ at $0°$ for the ${}^{90}\mathrm{Zr}\mathrm{}(p,n)\mathrm{}$ reaction are measured at a bombarding energy of 295 MeV. A multipole decomposition technique is applied to the cross sections to extract $L=0\mathrm{}$, $L=1\mathrm{}$, $L=2\mathrm{}$, and $L=3\mathrm{}$ contributions. The Gamow-Teller (GT) strength $B\left(\mathrm{GT}\right)$ in the continuum deduced from the $L=0\mathrm{}$ cross section is compared both with the perturbative calculation by Bertsch and Hamamoto and with the second-order random phase approximation calculation by Drożdż et al. The sum of $B\left(\mathrm{GT}\right)$ values up to 50 MeV excitation becomes $S_{{\beta }^{-}}$=28.0±1.6 after subtracting the contribution of the isovector spin-monopole strength. This $S_{{\beta }^{-}}$ value of 28.0$\pm$1.6 corresponds to about (93 $\pm$ 5)% of the minimum value of the sum rule $3\left(N-Z\right)$=30. The usefulness of the polarization transfer observable in the distorted wave impulse approximation is presented.