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

Abstract

The pairing properties of the neutrinoless double-β decay (0ν2β) candidate 100Mo have been studied, along with its daughter 100Ru, to provide input for nuclear matrix element calculations relevant to the decay. The (p, t ) two-neutron transfer reaction was measured on nuclei of 102,100Ru and 100,98Mo. The experiment was designed to have particular sensitivity to 0+ states up to excitation energies of ∼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 100Ru, greater than 95% of the L = 0 (p, t ) strength was in the ground state, but in 100Mo about 20% was in excited 0+ states. The measured (p, t ) data, together with existing (t,p) data, suggest that 100Mo is a shape-transitional nucleus while 100Ru is closer to the spherical side of that transition. Theoretical calculations of the 0ν2β nuclear matrix element may be complicated by this difference in shape.