Analysis and interpretation of a large body of 76Ge zero-neutrino double- beta -decay data.

Abstract

Data from five recent $^{76}\mathrm{Ge}$ double-\ensuremath{\beta}-decay experiments were combined in a single spectrum equivalent to counting for 0.4 yr with 1770-${\mathrm{cm}}^{3}$ fiducial volume of Ge. The composite spectrum was analyzed using an approximate analytical form of the likelihood function. The maximum likelihood 68%-C.L. values for the half-life and Majorana \ensuremath{\nu} mass are ${\mathit{T}}_{1/2}^{\mathit{O}\mathit{v}}$${(}^{76}$Ge)\ensuremath{\gtrsim}4.1\ifmmode\times\else\texttimes\fi{}${10}^{23}$ yr and 〈${m}_{\ensuremath{\nu}}$〉\ensuremath{\lesssim}2.4 eV, respectively, when accounting for the slight depression in the spectrum, and 2.4\ifmmode\times\else\texttimes\fi{}${10}^{23}$ yr and 〈${m}_{\ensuremath{\nu}}$〉\ensuremath{\lesssim}3.2 eV when neglecting the depression. It is clearly demonstrated that experiments with current levels of background will soon reach their point of diminishing returns.