Topologies of 76Ge double-beta decay events and calibration procedure biases

The analysis of the time profile of electrical signals produced by energy depositions in germanium detectors allows discrimination of events with different topologies. This is especially relevant for experiments searching for the neutrinoless double beta decay of Ge-76 to distinguish the sought-after signal from other background sources. The standard calibration procedures used to tune the selection criteria for double-beta decay events use a Th-228 source, because it provides samples of signal-like events. These samples exhibit energy spatial distributions with subtle different topologies compared to neutrinoless double-beta decay events. In this work, we will characterize these topological differences and, with the support of a Co-56 source, evaluate biases and precision of calibration techniques which use such event samples. Our results will be particularly relevant for future experiments in which a solid estimation of the efficiency is required.

Automated summary

The analysis of electrical signals produced by energy depositions in germanium detectors can distinguish events with different topologies, which is crucial for experiments searching for the neutrinoless double beta decay of Ge-76. Standard calibration procedures use a Th-228 source to tune selection criteria, but the energy spatial distributions of Th-228 events have subtle differences compared to double-beta decay events. This work characterizes these topological differences and evaluates calibration techniques using a Co-56 source, providing important insights for future experiments requiring reliable efficiency estimation.