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RESEARCH PRODUCT

Charge-exchange reactions on double-βdecaying nuclei populatingJπ=2−states

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The $(\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He},t)$ charge-exchange reaction populating ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$ states has been examined at 420 MeV incident energy for a series of double-$\ensuremath{\beta}$ decaying nuclei, i.e., $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{96}\mathrm{Zr}$, $^{100}\mathrm{Mo}$, $^{128}\mathrm{Te}$, $^{130}\mathrm{Te}$, and $^{136}\mathrm{Xe}$. The measurements were carried out at the Grand Raiden spectrometer of the Research Center for Nuclear Physics at the University Osaka with typical spectral resolution of 30--40 keV. It is found that the charge-exchange reaction leading to ${2}^{\ensuremath{-}}$ spin-dipole states is selective to the $\ensuremath{\sigma}\ensuremath{\tau}$ part of the interaction much similar to the observed selectivity to Gamow-Teller transitions. In the present case, the $\mathrm{\ensuremath{\Delta}}L=1$ peak cross sections at finite momentum transfers are used to extract the spin-isospin part of the low-lying transition strength near the Fermi surface (i.e., ${E}_{x}\ensuremath{\le}5$ MeV). Relative strength values are confronted with various model calculations, i.e., the interacting shell model, the quasiparticle random-phase approximation, and the Fermi surface quasiparticle model. The impact on the nuclear matrix elements for the neutrinoless double-$\ensuremath{\beta}$ decay is discussed.