Limits on neutrinolessββdecay, including that with majoron emission

Abstract

Neutrinoless double-β 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 $0^{+}$→$0^{+}$ transition in ${}_{}{}^{76}{}_{}{}^{}\mathrm{Ge}$ of $T_{1/2}$>5×${10}^{23}$ 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×${10}^{21}$ yr, a result in disagreement with a recent possible observation of majoron emission.