Searching for ${}^{76}$Ge neutrinoless double beta decay with the CDEX-1B experiment

Abstract

We operated a p-type point contact high purity germanium (PPCGe) detector (CDEX-1B, 1.008 kg) in the China Jinping Underground Laboratory (CJPL) for 500.3 days to search for neutrinoless double beta ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) decay of ${}^{76}$Ge. A total of 504.3 kg$\cdot$day effective exposure data was accumulated. The anti-coincidence and the multi/single-site event (MSE/SSE) discrimination methods were used to suppress the background in the energy region of interest (ROI, 1989$-$2089 keV for this work) with a factor of 23. A background level of 0.33 counts/(keV$\cdot$kg$\cdot$yr) was realized. The lower limit on the half life of ${}^{76}$Ge $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay was constrained as $T_{1/2}^{0\hat{I}½}>1.0\times 10^{23}\mathrm{yr}(90\%C.L.)$, corresponding to the upper limits on the effective Majorana neutrino mass: $⟨m_{{\hat{I}}^2{\hat{I}}^2}⟩<$3.2$-$7.5$\mathrm{eV}$.

11 pages, 12 figures, 2 tables. Version updated to match CPC version