Neutron pair correlations in A=100 nuclei involved in neutrinoless double-${\hat{I}}^2$ decay

Abstract

The pairing properties of the neutrinoless double beta decay $(0\nu 2{\hat{I}}^2)$ candidate ${}^{100}$Mo have been studied, along with its daughter ${}^{100}$Ru, to provide input for nuclear matrix element calculations relevant to the decay. The $(p,t)$ two-neutron transfer reaction was measured on nuclei of ${}^{102,100}$Ru and ${}^{100,98}$Mo. The experiment was designed to have particular sensitivity to $0^{+}$ states up to excitation energies of $\sim 3$ MeV with high energy resolution. Measurements were made at two angles and L=0 transitions identified by the ratio of yields between the two angles. For the reactions leading to and from ${}^{100}$Ru, greater than 95% of the L=0 $(p,t)$ strength was in the ground state, but in ${}^{100}$Mo about 20% was in excited $0^{+}$ states. The measured $(p,t)$ data, together with existing $(t,p)$ data, suggest that ${}^{100}$Mo is a shape-transitional nucleus while ${}^{100}$Ru is closer to the spherical side of that transition. Theoretical calculations of the $0\nu 2{\hat{I}}^2$ nuclear matrix element may be complicated by this difference in shape.

5 pages, 2 figures