Seminar Details

Neutron Scattering Studies Relevant to Neutrinoless Double Beta Decay

Ben Crider, University of Kentucky
Thursday, December 12, 11:00 AM - Research Discussion
NSCL Lecture Hall

The search for neutrinoless double-beta decay (0νββ) is the subject of large international effort, with hopes of discovering physics beyond the standard model. One candidate for the observation of 0νββ, the decay of 76Ge to 76Se, is the focus of two major collaborative experiments. In these experiments, the signature of 0νββ would appear as a sharp peak in the energy spectrum at 2039 keV. Due to the high sensitivity of such a measurement, knowledge of background γ rays is critical. One such concern is the 2040.70(25)-keV γ ray from the 3951.70(14)-keV level in 76Ge, found in a study of 76Ga β− decay. This state could be populated via cosmic-ray-induced inelastic neutron scattering in the large experiments searching for the 2039-keV signature of 0νββ. The neutron-induced cross section of this state then becomes an excellent candidate for study using inelastic neutron scattering at the University of Kentucky Accelerator Laboratory (UKAL). If evidence of 0νββ is indeed found, extracting the absolute mass scale of neutrinos requires that the nuclear matrix elements involved in the calculation are understood to a high degree of accuracy. In order for this accuracy to be achieved, precise knowledge of the levels involved, especially those of the daughter, 76Se, is required. In addition to their implications for 0νββ, 76Ge and 76Se also exhibit interesting nuclear structure such as mixed-symmetry states and shape coexistence in this mass region. In an effort to address the above questions, excitation function and γ-ray angular distribution measurements utilizing the 76Ge(n, nγ) and 76Se(n, n γ) reactions were performed at UKAL. As a result of analysis of these measurements, I will present information on level spins and parities, level lifetimes using the Doppler-shift attenuation method, transition multipolarities, and transition probabilities. Additionally, from the higher energy excitation functions, I have obtained values for the neutron-induced cross sections of the transitions from the 3951.70(14)-keV level in 76Ge. This material is based upon work that is supported by the U.S. National Science Foundation under grant no. PHY-0956310 and PHY-1305801.