Analysis and interpretation of a large body ofGe76zero-neutrino double-β-decay data

Abstract

Data from five recent ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$ double-β-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 ν mass are ${\mathit{T}}_{1/2}^{\mathit{O}\mathit{v}}$ ${(}^{76}$Ge)≳4.1×${10}^{23}$ yr and 〈$m_{\nu }$〉≲2.4 eV, respectively, when accounting for the slight depression in the spectrum, and 2.4×${10}^{23}$ yr and 〈$m_{\nu }$〉≲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.