Search for Neutrinoless Double-Beta Decay of $^{76}$Ge with a Natural Broad Energy Germanium Detector

TL;DR

This study demonstrates the feasibility of using a natural broad energy germanium detector in an underground lab to search for neutrinoless double-beta decay of $^{76}$Ge, achieving low background levels and setting new half-life limits.

Contribution

First application of a natural BEGe detector in CJPL for neutrinoless double-beta decay search, with improved background reduction and new half-life constraints.

Findings

Background index of 6.4×10⁻³ counts/(keV·kg·day) achieved

No decay signal observed in 186.4 kg·day exposure

Half-life limit set at >5.62×10²² years

Abstract

A natural broad energy germanium (BEGe) detector is operated in the China Jinping Underground Laboratory (CJPL) for a feasibility study of building the next generation experiment of the neutrinoless double-beta (0{$\nu\beta\beta$}) decay of $^{76}$Ge. The setup of the prototype facility, characteristics of the BEGe detector, background reduction methods, and data analysis are described in this paper. A background index of 6.4$\times$10$^{-3}$ counts/(keV$\cdot$kg$\cdot$day) is achieved and 1.86 times lower than our previous result of the CDEX-1 detector. No signal is observed with an exposure of 186.4 kg$\cdot$day, thus a limit on the half life of $^{76}$Ge 0$\nu\beta\beta$ decay is set at T$_{1/2}^{0\nu}$ $>$ 5.62$\times$10$^{22}$ yr at 90% C.L.. The limit corresponds to an effective Majorana neutrino mass in the range of 4.6 $\sim$ 10.3 eV, dependent on the nuclear matrix elements.