Nuclear Structure Relevant to Neutrinoless Double Beta Decay: the Valence Protons in 76Ge and 76Se

TL;DR

This study measures valence proton occupations in 76Ge and 76Se to improve nuclear matrix element calculations for neutrinoless double beta decay, revealing a more diffuse Fermi surface and significant orbital occupancy changes.

Contribution

It provides precise proton occupation data in 76Ge and 76Se, highlighting differences from previous models and aiding decay rate predictions.

Findings

Proton Fermi surface is more diffuse than previously thought.

Significant changes in orbital occupancies between 76Ge and 76Se.

Results impact theoretical calculations of neutrinoless double beta decay.

Abstract

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain and the occupations of valence orbits by nucleons active in the decay are likely to be important. The occupation of valence proton orbits in the ground states of 76Ge, a candidate for such decay, and 76Se, the corresponding daughter nucleus, were determined by precisely measuring cross sections for proton-removing transfer reactions. As in previous work on neutron occupations, we find that the Fermi surface for protons is much more diffuse than previously thought, and the occupancies of at least three orbits change significantly between the two 0+ ground states.