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 to search for the neutrinoless double-beta (0νββ) decay of 76 Ge in the China Jinping Underground Laboratory (CJPL). 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 6.4×10 −3 counts/(keV•kg•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•day, thus a limit on the half life of 76 Ge 0νββ decay is set at T 0ν 1/2 > 5.62×10 22 yr at 90% C.L.. The limit corresponds to an effective Majorana neutrino mass in the range of 4.6 ∼ 10.3 eV, dependent on the nuclear matrix elements.