Nuclear structure relevant to neutrinoless doubleβdecay: The valence protons inGe76and

B. P. Kay

¹

,

J. P. Schiffer

²

,

S. J. Freeman

³

et al.

Abstract

The possibility of observing neutrinoless double β 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 76 Ge, a candidate for such decay, and 76 Se, 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.

Coulomb excitation ofGa73

“…As this state is populated directly by Coulomb excitation, the spin can be firmly fixed as 5/2 − . A recent 74 Ge(d, 3 He) transfer reaction using polarized deuterons also favors a 5/2 − assignment for this state [26,27].…”

Occupation probabilities of single particle levels using the microscopic interacting boson model: Application to some nuclei of interest in neutrinoless double-βdecay

“…In the case of 76 Ge and 76 Se both neutron vacancies and proton occupancies have been determined recently by accurate measurements of one-nucleon transfer reactions [1,2]. The theoretical IBM-2 occupancies are shown in Figs.…”

“…Through the analysis of the experimental spectroscopic factors of stripping and pick-up reactions the occupation numbers of the orbits close to the Fermi level can be extracted. This has been recently done, or is under investigation at the moment, for neutrons or for both neutrons and protons in 76 Ge, 76 Se, 100 Mo, * jenni.kotila@jyu.fi † jbarea@udec.cl 100 Ru, 130 Te, 130 Xe, 136 Xe, 136 Ba, 150 Nd, and 150 Sm in a series of very careful experiments [1][2][3][4][5]. These nuclei are candidates to participate in neutrinoless double-β decay and recently the role of the chosen single-particle valence space and orbital occupancies has also become one of the central issues in the calculation of the double-β-decay nuclear matrix elements (NMEs) [1,2,[6][7][8].…”

“…This has been recently done, or is under investigation at the moment, for neutrons or for both neutrons and protons in 76 Ge, 76 Se, 100 Mo, * jenni.kotila@jyu.fi † jbarea@udec.cl 100 Ru, 130 Te, 130 Xe, 136 Xe, 136 Ba, 150 Nd, and 150 Sm in a series of very careful experiments [1][2][3][4][5]. These nuclei are candidates to participate in neutrinoless double-β decay and recently the role of the chosen single-particle valence space and orbital occupancies has also become one of the central issues in the calculation of the double-β-decay nuclear matrix elements (NMEs) [1,2,[6][7][8]. As major experimental efforts are being made in the search for massive Majorana neutrinos and their absolute mass scale through the process of neutrinoless double-β decay, the calculation of these NMEs is an essential step in the study of 0νββ decay, which is crucial for extracting the neutrino mass from experimental half-life.…”

A measurement of the 2 neutrino double beta decay rate of Te-130 in the CUORICINO experiment

“…However, one promising new avenue of experimental input was explored by recent measurements of the neutron and proton valence occupancies in the ground states of 76 Ge and 76 Se via nucleon transfer reactions ( [25], [26]). These measurements were found to be in significant disagreement with the QRPA and ISM models used for ββ decay calculations.…”