Prototyping and Operation of a Basic Module for the COBRA Double Beta Experiment

• Applicants: Professor Dr. Claus Gößling; Professor Dr. Kai Zuber
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 268689691

The goal of this application is the commissioning, test and lowbackground operation of the Detector-Basic-Module for the COBRA-Large-Array setup. The module will consist of nine 6cm^3 CdZnTe-Detectors in Quad-CPG configuration (CPG-CoPlanarGrid). This prototype represents the Basic-Module for a suggested large scale setup. With this Large-Array it shall be possible to prove the existence of the neutrinoless double beta decay with the COBRA-Experiment.The applied crystals will have a six times larger volume compared to the ones used in the COBRA-Demonstrator. This will result in a clear reduction of the surface induced background contribution by the nearly bisected surface-to-volume ratio. Furthermore, the total efficiency will increase due to the generally larger volume of the detector and, hence, increase the sensitivity of the whole experiment. Therefore, in the first work package, as yet developed methods and algorithms have to be transferred to the advanced geometry of the new detectors.Besides the clearly identifiable surface events a major background contribution originates from Multi-Site interactions in the crystal. The change from the single CPG (used in the COBRA-Demonstrator) to the Quad-CPG makes it possible to improve the discrimination power between Single- and Multi-Site events. Hence, in the second work-package the already available identification algorithms have to be adapted to the new anode layout and a decision has to be made to fix the final anode geometry.In addition to the detector based investigations the engineering of the mechanical parts is continued too. So it has to be ensured that the future Large-Array can be assembled from the constructed Detector-Basis-Module. Another important prerequisite for a scale-up of the experiment is the transition from the discrete pulse-shape sampling to an integrated, ASIC-based data acquisition. For this purpose a suitable system has been purchased. This system mainly fulfills the requirements but has to be adapted to the special needs of COBRA. This work will also be done during the funding period.Finally, the completely assembled Detector-Module will be installed in the underground laboratory LNGS (Italy). It has to be proven, that the new approach allows for the reduction of the background index, such, that the COBRA-Experiment becomes a competitive experiment for the search for the neutrinoless double beta decay.

• DFG Programme: Research Grants