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 (0νββ) decayof ⁷⁶Ge. A total of 504.3 kg 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. Abackground level of 0.33 counts/(keV kg yr) was realized. The lower limit onthe half life of ⁷⁶Ge (0νββ)decay was constrained as T_1/20v > 1.0×10²³yr(90% C.L.), corresponding to the upper limits on the effective Majorana neutrino mass: <m_ββ> < 3.2—7.5 eV.

Keywords: neutrinoless double beta decay, CDEX, point-contact germanium detector, ⁷⁶Ge

doi: 10.1088/1674-1137/ad597b