Results of a search for neutrinoless double-beta decay using the COBRA demonstrator

Abstract

Neutrinoless double-${\hat{I}}^2$ decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay) is a hypothetical process that can occur if the neutrino is its own antiparticle. The COBRA collaboration operates a demonstrator to search for these decays at the Laboratori Nazionali del Gran Sasso in Italy using CdZnTe semiconductor detectors. The exposure of $234.7$kg\,d considered in this analysis was collected between September 2011 and February 2015. The analysis focuses on the decay of the nuclides ${}^{114}$Cd, ${}^{128}$Te, ${}^{70}$Zn, ${}^{130}$Te and ${}^{116}$Cd. A Bayesian analysis is performed to estimate the signal strength of $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay. No signal is observed for any of these nuclides. Therefore, the following half-life limits at 90% credibility are set: $T_{1/2}^{0\hat{I}½}>1.6\cdot 10^{21}$yr (${}^{114}$Cd), $T_{1/2}^{0\hat{I}½}>1.9\cdot 10^{21}$yr (${}^{128}Te$), $T_{1/2}^{0\hat{I}½}>6.8\cdot 10^{18}$yr (${}^{70}$Zn), $T_{1/2}^{0\hat{I}½}>6.1\cdot 10^{21}$yr (${}^{130}$Te), and $T_{1/2}^{0\hat{I}½}>1.1\cdot 10^{21}$yr (${}^{116}$Cd).

7 pages, 8 figures and 3 tables, accepted by Phys. Rev. C