The first result on 76Ge neutrinoless double beta decay from CDEX-1 experiment

TL;DR

This paper reports the first experimental search for neutrinoless double beta decay in Ge-76 using the CDEX-1 detector, setting new limits on decay half-life and neutrino mass.

Contribution

It presents the first results from the CDEX-1 experiment on Ge-76 neutrinoless double beta decay, including new half-life limits and background analysis methods.

Findings

Half-life > 6.4×10^22 years at 90% CL

Effective Majorana neutrino mass limit of 5.0 eV

Background reduction strategies discussed

Abstract

We report the first result on Ge-76 neutrinoless double beta decay from CDEX-1 experiment at China Jinping Underground Laboratory. A mass of 994 g p-type point-contact high purity germanium detector has been installed to search the neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304 kg*day has been analyzed. The wideband spectrum from 500 keV to 3 MeV was obtained and the average event rate at the 2.039 MeV energy range is about 0.012 count per keV per kg per day. The half-life of Ge-76 neutrinoless double beta decay has been derived based on this result as: T 1/2 > 6.4*10^22 yr (90% C.L.). An upper limit on the effective Majorana-neutrino mass of 5.0 eV has been achieved. The possible methods to further decrease the background level have been discussed and will be pursued in the next stage of CDEX experiment.