First results on double beta decay modes of Cd, Te and Zn isotopes with the COBRA experiment

TL;DR

This study demonstrates the feasibility of using CdZnTe semiconductor detectors in the COBRA experiment to search for double beta decay, achieving promising energy resolution and setting new lower limits on decay half-lives.

Contribution

First experimental results on double beta decay modes of Cd, Te, and Zn isotopes using CdZnTe detectors in the COBRA setup, with improved half-life limits and background understanding.

Findings

Achieved energy resolutions capable of suppressing two-neutrino double beta decay background.

Developed a background model using Monte Carlo simulations and contamination measurements.

Set new lower limits on neutrinoless double beta decay half-lives for multiple isotopes.

Abstract

Four 1cm^3 CdZnTe semiconductor detectors were operated in the Gran Sasso National Laboratory to explore the feasibility of such devices for double beta decay searches as proposed for the COBRA experiment. The research involved background studies accompanied by measurements of energy resolution performed at the surface. Energy resolutions sufficient to reduce the contribution of two-neutrino double beta decay events to a negligible level for a large scale experiment have already been achieved and further improvements are expected. Using activity measurements of contaminants in all construction materials a background model was developed with the help of Monte Carlo simulations and major background sources were identified. A total exposure of 4.34 kg.days of underground data has been accumulated allowing a search for neutrinoless double beta decay modes of seven isotopes found in CdZnTe. Half-life limits (90% C.L.) are presented for decays to ground and excited states. Four improved lower limits have been obtained, including zero neutrino double electron capture transitions of Zn64 and Te120 to the ground state, which are 1.19*10^{17} years and 2.68*10^{15} years respectively.