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

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{$\hat{I}½{\hat{I}}^2{\hat{I}}^2$}) 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$\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay is set at T${}_{1/2}^{0\hat{I}½}$ $>$ 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.

10 pages, 15 figures