Quasi Random Phase Approximation Predictions on Two-Neutrino Double Beta Decay Half-Lives to the First 2 ⁺ State

Abstract

Two-neutrino double beta decay (2𝜈𝛽𝛽) half-lives to the first excited state are calculated in the framework of quasi random phase approximation. The quadrupole transition probabilities and the 2𝜈𝛽𝛽 decay amplitudes to the final ground states are reproduced by using adjustable parameters. The obtained half-lives are compared with the corresponding experimental data.

The Majorana Demonstrator's Search for Double-Beta Decay of $^{76}$Ge to Excited States of $^{76}$Se

“…The most recent predictions for the 2 + 1 e.s. range using RQRPA [53][54][55][56] and EFT [51] techniques yield half-lives in excess of 1.0 × 10 26 y, well beyond the reach of the Majorana Demonstrator. Similarly, a calculation using RQRPA for the 2 + 2 e.s.…”

“…By comparing the rate of multiplicity-1 events in the SEPs and DEPs to the rate of multiplicity-2 events in which one hit falls into one of these peaks and the other falls into the 511 keV peak, we can measure a proxy for the detection efficiency of our multi-detector event signature. 56 Co produces a large number of γs at energies high enough to cause pair production, which allows for a comparison of many peaks to our simulation. This comparison was performed using 168.1 h and 167.1 h of data with the 56 Co line source inserted into the Module 1 and Module 2 calibration tracks, respectively, and a simulation of 3 billion event primaries generated by MaGe.…”

“…Once per week, 228 Th sources are deployed into each track, one at a time, for 90 min. In addition, in January 2019, a 56 Co line source with a nominal activity of 6 kBq was deployed in each track for one week at a time. This source emits many γ rays with an energy of > 1.5 MeV, which produce inherently multisite pair production events that are useful for systematic checks.…”

“…Uncertainties are applied as if they are statistically independent. The domininant sources of uncertainty come from the dead layer thickness and the error found in the 56 Co spectral comparisons. Using these simulations, the detection efficiency for the 2νββ to 0 + 1 e.s.…”

Two neutrino double-$β$ decay of $94\leq A\leq 150$ nuclei for the 0$^{+}\rightarrow $2$^{+}$ transition

“…The marked variation in the theoretically calculated NTMEs M 2ν (2 + ) for the 0 + → 2 + transition using different nuclear models is a general feature [8]. For example, the available results for M 2ν (2 + ) of 96 Zr show that the calculated NTMEs within QRPA [14,15,16], RQRPA(WS) [17], RQRPA (AWS) [17], and SRPA(WS) [18], differ by a factor of 341. Hence, the observation of the 0 + → 2 + transition of 2νβ − β − de-cay can constrain the validity of different nuclear models employed in the calculation of NTMEs.…”