Experimental study of double-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>β</mml:mi></mml:mrow></mml:math>decay modes using a CdZnTe detector array

An array of sixteen $1 {\mathrm{cm}}^{3}$ CdZnTe semiconductor detectors was operated at the Gran Sasso Underground Laboratory (LNGS) to further investigate the feasibility of double-$\ensuremath{\beta}$ decay searches with such devices. As one of the double-$\ensuremath{\beta}$ decay experiments with the highest granularity the $4\ifmmode\times\else\texttimes\fi{}4$ array accumulated an overall exposure of $18 \mathrm{kg} \mathrm{days}$. The setup and performance of the array is described. Half-life limits for various double-$\ensuremath{\beta}$ decay modes of Cd, Zn, and Te isotopes are obtained. No signal has been found, but several limits beyond ${10}^{20} \mathrm{years}$ have been performed. They are an order of magnitude better than those obtained with this technology before and comparable to most other experimental approaches for the isotopes under investigation. An improved limit for the ${\ensuremath{\beta}}^{+}$/EC decay of $^{120}\mathrm{Te}$ is given.