Limits on neutrinoless<i>ββ</i>decay, including that with majoron emission

Abstract

Neutrinoless double-\ensuremath{\beta} decay would require two new phenomena, of which one is lepton-number nonconservation. Among several candidates for the other are nonzero neutrino mass and the emission of a Goldstone boson, such as the majoron. For the former possibility our Ge-detector array now sets a limit for the ${0}^{+}$\ensuremath{\rightarrow}${0}^{+}$ transition in $^{76}\mathrm{Ge}$ of ${T}_{1/2}$&gt;5\ifmmode\times\else\texttimes\fi{}${10}^{23}$ yr from the fluctuation in the background or almost a factor of 2 longer by maximum likelihood at the 68% confidence level (C.L.). For the latter process we have a 90%-C.L. limit of 1.4\ifmmode\times\else\texttimes\fi{}${10}^{21}$ yr, a result in disagreement with a recent possible observation of majoron emission.