Neutron pair correlations in A=100 nuclei involved in neutrinoless double-$\beta$ decay

TL;DR

This study investigates neutron pair correlations in $^{100}$Mo and $^{100}$Ru to inform nuclear matrix element calculations for neutrinoless double-beta decay, revealing shape differences that could impact theoretical models.

Contribution

It provides new experimental data on neutron pair transfer reactions in $^{100}$Mo and $^{100}$Ru, highlighting shape transitional behavior relevant to decay calculations.

Findings

Most L=0 strength in $^{100}$Ru is in the ground state.

Approximately 20% of L=0 strength in $^{100}$Mo is in excited $0^{+}$ states.

$^{100}$Mo is a shape-transitional nucleus, while $^{100}$Ru is near spherical.

Abstract

The pairing properties of the neutrinoless double beta decay $(0\nu2\beta)$ 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 $0\nu2\beta$ nuclear matrix element may be complicated by this difference in shape.