Calculation of Sensititvity to Neutrinoless Double Beta Decay for COBRA Demonstrator

AbstraktAbstract

The goal of this diploma thesis is to calculate half-life sensitivities (T1/2) of the COBRA experiment to neutrinoless double-beta decay for four different isotopes (ground state to ground state transitions): Te-128 (Q = 865.9 keV), Zn-70 (Q = 998.5 keV), Te-130 (Q = 2527.0 keV), and Cd-116 (Q = 2813.5 keV). COBRA experiment is an experiment searching for neutrino-less double-beta decay using array of 64 cubic CdZnTe semiconductor detectors of 1 cm3 volume each. Analysis is based on the data from the first phase of the project, so-called COBRA Demonstrator, collected between 2013 and 2019 (total exposure of 1.252 kg.yr). The Dataset was split into subsets called partitions and, in order to obtain the optimal regions of interest for each individual partition, optimized window counting method was employed. The detector signal count sensitivities were calculated using the author´s own implementation of Feldman and Cousins method. In comparison to Bayesian analysis from 2016, we received improved half-life sensitivities for Te-130 (T1/2 ≥ 6.9 · 10^21 yr) and Cd-116 (T1/2 ≥ 1.8 · 10^21 yr). Worse limits were obtained for Te-128 (T1/2 ≥ 1.8·10^21 yr) and Zn-70 (T1/2 ≥ 4.9·10^18 yr). The worse limits for Te-128 and Zn-70 can be accounted for the different values of isotope abundances used in the article and the presented thesis as well as the oversimplified background model. The uncertainties of the experimental parameters were omitted and should be included in future work in order to obtain more robust results.

The goal of this diploma thesis is to calculate half-life sensitivities (T1/2) of the COBRA experiment to neutrinoless double-beta decay for four different isotopes (ground state to ground state transitions): Te-128 (Q = 865.9 keV), Zn-70 (Q = 998.5 keV), Te-130 (Q = 2527.0 keV), and Cd-116 (Q = 2813.5 keV). COBRA experiment is an experiment searching for neutrino-less double-beta decay using array of 64 cubic CdZnTe semiconductor detectors of 1 cm3 volume each. Analysis is based on the data from the first phase of the project, so-called COBRA Demonstrator, collected between 2013 and 2019 (total exposure of 1.252 kg.yr). The Dataset was split into subsets called partitions and, in order to obtain the optimal regions of interest for each individual partition, optimized window counting method was employed. The detector signal count sensitivities were calculated using the author´s own implementation of Feldman and Cousins method. In comparison to Bayesian analysis from 2016, we received improved half-life sensitivities for Te-130 (T1/2 ≥ 6.9 · 10^21 yr) and Cd-116 (T1/2 ≥ 1.8 · 10^21 yr). Worse limits were obtained for Te-128 (T1/2 ≥ 1.8·10^21 yr) and Zn-70 (T1/2 ≥ 4.9·10^18 yr). The worse limits for Te-128 and Zn-70 can be accounted for the different values of isotope abundances used in the article and the presented thesis as well as the oversimplified background model. The uncertainties of the experimental parameters were omitted and should be included in future work in order to obtain more robust results.