Search for neutrinoless double-beta decay of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Ge</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>76</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> with a natural broad energy germanium detector

Abstract

A natural broad energy germanium detector is operated in the China Jinping Underground Laboratory for a feasibility study of building the next generation experiment of the neutrinoless double-beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay of $^{76}\mathrm{Ge}$. The setup of the prototype facility, characteristics of the broad energy germanium detector, background reduction methods, and data analysis are described in this paper. A background index of $6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{counts}/(\mathrm{keV}\text{ }\mathrm{kg}\text{ }\mathrm{day})$ 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 $^{76}\mathrm{Ge}$ $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay is set at ${\mathrm{T}}_{1/2}^{0\ensuremath{\nu}}&gt;5.62\ifmmode\times\else\texttimes\fi{}{10}^{22}\text{ }\text{ }\mathrm{yr}$ 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.