First Results of the Search for Neutrinoless Double-Beta Decay with the NEMO 3 Detector

Abstract

The NEMO 3 detector, which has been operating in the Fr\'ejus underground laboratory since February 2003, is devoted to the search for neutrinoless double-beta decay ($\ensuremath{\beta}\ensuremath{\beta}0\ensuremath{\nu}$). The half-lives of the two neutrino double-beta decay ($\ensuremath{\beta}\ensuremath{\beta}2\ensuremath{\nu}$) have been measured for $^{100}\mathrm{Mo}$ and $^{82}\mathrm{Se}$. After 389 effective days of data collection from February 2003 until September 2004 (phase I), no evidence for neutrinoless double-beta decay was found from $\ensuremath{\sim}7\text{ }\text{ }\mathrm{kg}$ of $^{100}\mathrm{Mo}$ and $\ensuremath{\sim}1\text{ }\text{ }\mathrm{kg}$ of $^{82}\mathrm{Se}$. The corresponding limits are ${T}_{1/2}(\ensuremath{\beta}\ensuremath{\beta}0\ensuremath{\nu})>4.6\ifmmode\times\else\texttimes\fi{}{10}^{23}\text{ }\mathrm{yr}$ for $^{100}\mathrm{Mo}$ and ${T}_{1/2}(\ensuremath{\beta}\ensuremath{\beta}0\ensuremath{\nu})>1.0\ifmmode\times\else\texttimes\fi{}{10}^{23}\text{ }\mathrm{yr}$ for $^{82}\mathrm{Se}$ (90% C.L.). Depending on the nuclear matrix element calculation, the limits for the effective Majorana neutrino mass are $⟨{m}_{\ensuremath{\nu}}⟩<0.7--2.8\text{ }\text{ }\mathrm{eV}$ for $^{100}\mathrm{Mo}$ and $⟨{m}_{\ensuremath{\nu}}⟩<1.7--4.9\text{ }\text{ }\mathrm{eV}$ for $^{82}\mathrm{Se}$.