Gamow-Teller strength of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>90</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Nb in the continuum studied via multipole decomposition analysis of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow/><mml:mrow><mml:mn>90</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Zr<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn/><mml:mo>(</mml:mo><mml:mi>p</mml:mi><mml:mo>,</mml:mo><mml:mi>n</mml:mi><mml:mo>)</mml:mo><mml:mn/></mml:math>reaction at 295 MeV

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