Simulation Study on the Discrimination of $0\nu\beta\beta$ Events from Single-Electron Events Using Orthogonal-Strip HPGe Detectors

TL;DR

This study uses simulations and neural networks to evaluate how orthogonal-strip HPGe detectors can distinguish neutrinoless double beta decay events from single-electron backgrounds, guiding detector design for neutrino research.

Contribution

The paper develops a simulation framework combining Geant4 and charge cloud modeling, and applies CNNs to assess and optimize detector geometry for background discrimination.

Findings

Discrimination efficiency decreases with larger strip pitch.

Optimal crystal thickness balances efficiency and discrimination.

Detectors can effectively suppress single-electron backgrounds.

Abstract

Neutrinoless double beta decay ($0\nu\beta\beta$) offers a sensitive probe of neutrino mass and its Majorana nature. Orthogonal-strip high-purity germanium (HPGe) detectors with high spatial resolution provide a promising approach for distinguishing $0\nu\beta\beta$ events from single-electron backgrounds. In this work, a simulation framework was developed to evaluate the discrimination performance of these detectors. The framework combined Geant4 simulations with a hybrid numerical-analytical approach to model charge cloud dynamics. A dual-branch convolutional neural network (CNN) was implemented to extract topological features for event classification. The impact of detector geometry on discrimination performance was quantitatively assessed. For a fixed crystal thickness of 15 mm, the background rejection efficiency decreased from 79.5\% to 59.0\% as the strip pitch increased from 0.1 mm to 0.5 mm. For a strip pitch of 0.25 mm, a crystal thickness of 20 mm was found to be optimal, balancing full-energy peak (FEP) efficiency with discrimination capability. These results demonstrate that orthogonal-strip HPGe detectors can effectively suppress single-electron backgrounds, and provide quantitative guidance for detector design in $^{76}$Ge $0\nu\beta\beta$ decay searches.