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

Abstract

Neutrinoless double-$β$ decay ($0νββ$ 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 $0νββ$ decay. No signal is observed for any of these nuclides. Therefore, the following half-life limits at 90% credibility are set: $T_{1/2}^{0ν}>1.6\cdot10^{21}\,$yr ($^{114}$Cd), $T_{1/2}^{0ν}>1.9\cdot10^{21}\,$yr ($^{128}Te$), $T_{1/2}^{0ν}>6.8\cdot10^{18}\,$yr ($^{70}$Zn), $T_{1/2}^{0ν}>6.1\cdot10^{21}\,$yr ($^{130}$Te), and $T_{1/2}^{0ν}>1.1\cdot10^{21}\,$yr ($^{116}$Cd).